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Support for Data Reduction Attributes in nfsv4 Version 2

Document Type Active Internet-Draft (individual)
Authors Sorin Faibish , Philip Shilane , Ivan Basov
Last updated 2022-12-13
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NFSv4                                                         S. Faibish
Internet-Draft                                Cirrus Data Solutions Inc.
Intended status: Informational                                P. Shilane
Expires: June 12, 2023                                          Dell EMC
                                                                I. Basov
                                                       December 13, 2022

    Support for Data Reduction Attributes in nfsv4 Version 2


   This document proposes extending NFSv4 operations to add new 
   RECOMMENDED attributes to be used in the protocol to provide 
   information about the data reduction properties of files. The new 
   data reduction attributes are proposed to allow the client 
   application to communicate to the NFSv4 server data reduction 
   attributes associated with files and directories using new metadata, 
   communicated to the Block Storage data reduction engines. 
   Corresponding new RECOMMENDED attributes are proposed to allow 
   clients and client applications to query the server for data 
   reduction attributes support and allow to get and set data reduction
   attributes on files and directories. Such data reduction 
   metadata is used as hints to the file server about what type of data 
   reduction to apply. The proposed data reduction attributes include 
   achievable ratios for compression and deduplication plus whether 
   each data reduction technique applies to a file or directory.       

Status of This Memo

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   This Internet-Draft will expire on June 12, 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
   publication of this document.  Please review these documents
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Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3. New RECOMMENDED attributes  . . . . . . . . . . . . . . . . .   8
   4. File System Support . . . . . . . . . . . . . . . . . . . . .   9
   5. Namespaces  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   6. Data Reduction RECOMMENDED attributes . . . . . . . . . . . .  10
   7. Protocol Enhancements . . . . . . . . . . . . . . . . . . . .  11
   8. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . .  11
        10.1. Normative References  . . . . . . . . . . . . . . . .  11
        10.2  Informative References . . . . . . . . . . . . . . . . 12
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 12

1. Introduction

   Many NFS servers use expensive solid state media, e.g., NVMe SSDs, 
   complemented by data reduction processing of files to reduce their 
   size on the Block Storage via compression and deduplication, thereby 
   optimizing media usage. This draft considers scenarios in which 
   data reduction processing is performed in Block Storage for NFS 
   servers, i.e., compression and deduplication processing occurs in 
   the background or inline as a consequence of NFS files being 
   written to the Block Storage. In these scenarios, the data reduction 
   engines in Block Storage have limited information about how 
   reducible (compressible and/or deduplicate-able) the data written 
   to NFS is.
   There is additional strong interest to improve data reduction when 
   using NVMe accessed media and exposing such data attributes to the 
   Block Storage as files or directory attributes over NFS is one 
   means of providing this critical information to Block Storage data 
   reduction engines.

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   There is an expired draft for use of NVMe (over fabric) in accessing 
   a pNFS SCSI Layout [3] which could will be extended to communicate 
   data reduction attributes to NVMe storage. The shortcoming of the 
   current pNFS SCSI NVMe layout is that it has no information related 
   to data reduction attributes. This document discusses potential use 
   of NFSv4 RECOMMENDED attributes as currently standardized in [2], 
   for communicating additional data reduction metadata; a future 
   version of this document will propose updates to the NFSv4 protocol 
   to support this functionality. 

   The purpose of this draft is to define new RECOMMENDED attributes 
   that will allow applications to send richer metadata information 
   to the NFS server in order to optimize Block Storage data 
   reduction engine operations and improve data reduction for data 
   stored by NFS servers.  

   Applications can handle files with different compression and 
   deduplication characteristics and send this information to the data 
   reduction engines. Current applications have defined data reduction
   characteristics and there are clear definitions for the typical
   compression and deduplication ratios of some types of data 
   independent of the application that generated the data. For example 
   electronic data analysis (EDA) has no single de facto standard file 
   extension but generates application files with common compression 
   and deduplication characteristics. Knowing that a file is compressed 
   improves the latency and/or throughput of the NFS server by not 
   attempting to further compress the files.  An additional example is 
   that  NFS backup of files that are already stored on the Block 
   Storage is likely to result in a very high deduplication ratio. 

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [1].

   In this document, these words will appear with that interpretation  
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance. We will refer to the 
   block devices used by the NFS servers as "Block Storage". 

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2. Use Cases

   Applications can use RECOMMENDED attributes to store metadata 
   together with the files and directories. Metadata regarding data 
   reduction attributes may be available from applications that use 
   different types of files. This metadata may not be directly useful 
   to the file system but is relevant to the compression and 
   deduplication engines used by the Block Storage to improve data 
   reduction. Use of data reduction metadata is not expected to 
   significantly impact I/O latency or throughput (IOPS).

                         File Domain | Block Domain         
          +-------------+            |          +-----------------+
          | NFS Server  |------------|--------->|Reduction Engine |
          +------+------+            |          +--------+--------+
                 ^                   |                   | 
                 |                   |                   | 
                 |                   |                   v
          +------+------+            |          +--------+--------+
          | NFS Client  |            |          | Block storage   |
          +------+------+            |          +-----------------+
                 ^                   |                 
                 |                   |
                 |                   |
          +------+------+            |
          | Application |            |
          +-------------+            |
                 Figure 1: Data Reduction Domains for NFSv4

   Figure 1 shows the NFSv4 server configuration, data flow and 
   functionality domains with the data reduction engine in the Block 
   domain and located above the Block Storage. This figure represents 
   NFSv4 without parallel NFS (pNFS) support. In this structure the NFS 
   server can communicate RECOMMENDED attributes as metadata directly 
   to the Reduction Engine via an extension to the interface to Block 

   In general applications using block devices rely on SCSI protocols 
   to access the data. Although SCSI protocols have a rich API, most 
   communication between hosts and Block Storage, e.g., storage arrays, 
   is in terms of blocks, not files. In contrast applications use large
   files to read and write data to and from NFS servers. In general, 
   NFS servers use NFS file systems that are stored on SCSI (or NVMe) 
   devices provisioned from Block Storage, e.g., external storage 
   arrays, as Block Storage but file metadata, e.g., file type and file 
   size, is not transferred to the block array in a explicit manner.

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   An NFS Server might be able to infer data reduction characteristics 
   based on the file type, e.g., a ".mp4" file can be expected to be an 
   MP4 file that contains MPEG-4 content [7]. This is not sufficient 
   due to file content variability, e.g., as a large variety of codecs 
   are used to create MPEG-4 content whose compressibility may vary by 
   codec. To go beyond the file type, the NFS Server could read the 
   file contents to determine compressibility, but this is problematic 
   due to complexity, e.g., the NFS Server may need to parse a 
   significant amount of an MP4 file to obtain the information 
   necessary to understand its compressibility characteristics. This 
   may be impractical if the file is not written to the NFS Server 
   sequentially, and moreover introduces an undesirable dependency on 
   not only the MP4 file format, but also the set of supported codecs 
   that it supports and individual codec characteristics. It is much 
   better to have the application provide information on 
   compressibility, as the application that generates an MP4 file has 
   the information on the file's contents. A mechanism is needed to 
   pass that information to the NFS Server; this document proposes 
   adding and using new RECOMMENDED attributes.

   So, although the attributes are stored with the files, the current 
   NFSv4 RECOMMENDED attributes specifications [4] indicates that named 
   attributes are accessed by the OPENATTR operation, which accesses a 
   hidden directory of attributes associated with a file system object
   and contains files whose names represent the RECOMMENDED attributes 
   and whose data bytes are the value of the attribute. If the NFS 
   server extracts the data reduction RECOMMENDED attributes and pass 
   their contents to the Block Storage functionality, the Block Storage 
   reduction engines could parse that content and adapt its data 
   reduction behavior accordingly.  

                               File Domain |    Block Domain                  
          +-------------+                  |      +------------------+
          |             |------------------|----->|                  |
          | pNFS Server |          +-------|----->| Reduction Engine | 
          |             |          |  +----|----->|                  | 
          +------+------+          |  |    |      +---------+--------+
                 ^                 |  |    |                | 
                 |                 |  |    |                | 
                 |                 |  |    |                v
          +------+------+  NVMe    |  |    |       +--------+--------+
          | pNFS Client |----------+  |    |       | Block storage   |
          |             |-------------+    |       +-----------------+
          +------+------+  SCSI            |            
                 ^                         |
                 |                         |
                 |                         |
          +------+------+                  |
          | Application |                  |
          +-------------+                  |
          Figure 2: Data Reduction Domains for pNFS over NVMe or SCSI

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   The RECOMMENDED data reduction attributes may not be supported on 
   all clients and servers. A client may ask for any of these 
   attributes to be returned by setting a bit in the GETATTR request 
   but must handle the case where the server does not return them. A 
   client MAY ask for the set of attributes the server supports and 
   SHOULD NOT request attributes the server does not support. It is 
   expected that servers will support all attributes they comfortably 
   can and only fail to support attributes that are difficult to 
   support in their operating environments.

   The RECOMMENDED attributes are requested by setting a bit in the 
   bit vector sent in the GETATTR request; the server response includes
   a bit vector to list what attributes were returned in the response.
   The current situation is that data reduction done in the block 
   domain lacks critical information that could be provided by the 
   applications in order to improve efficiency of data compression and 

   Figure 2 shows another scenario with a pNFS Server and a block pNFS 
   Client that accesses Block storage using either NVMe or SCSI 
   over a network. In this scenario the pNFS Client could send data 
   reduction attributes directly to the reduction engine above the 
   Block storage layer if the block storage protocol (NVMe or SCSI in 
   the figure) supports doing so. The assumption is that the 
   application has additional information related to files types and 
   typical compression and deduplication parameters associated to 
   different file types, e.g., see the above discussion of MPEG-4 
   content. The application can convey this information to the 
   reduction engine to improve the reduction engine efficiency. If the 
   application does not do so, then the user can also add data 
   reduction characteristics for individual files towards improving 
   data reduction efficiency without needing to change the storage 
   array configuration. 
   For this pNFS scenario the application enables sending data 
   reduction parameters to the Block Device using extensions to the 
   SCSI or NVMe protocols. The pNFS Client still needs to pass the 
   data reduction RECOMMENDED attributes to the pNFS Server because 
   the pNFS Client is always allowed to fall back from a pNFS write 
   to an NFS write via the NFS Server; this fallback is similar to the 
   previous case where the NFS Server stores the data reduction 
   attributes associated with each file and directory. A server SHOULD 
   be tolerant of requests for unsupported attributes and simply not 
   return them rather than considering the request an error.    
   For example a video application knows whether a file consists of 
   compressed data or uncompressed data. The application writing the
   data to the pNFS client can set a RECOMMENDED attribute that will 
   indicate that a file is uncompressed and hence it is likely to be 
   productive for the data reduction engine to reduce the file's size.

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   The pNFS client passes that information via a RECOMMENDED attribute 
   that hints that the file is compressible. The pNFS server will 
   change or add a new data reduction attribute and will transmit the 
   data bytes, that are the value of the attribute, to the 
   Block Storage as a hint that the data is uncompressed. The pNFS 
   client will stream the video using the pNFS NVMe data protocol and 
   the compression engine in the Block Storage will compress the data 
   blocks as long as the uncompressed hint is set in NVMe writes from 
   the pNFS Client. If the attributes data bytes are changed 
   to indicate that the data has been compressed, the compression 
   engine does not compress the incoming blocks.

   A second example is related to encrypted files that can be neither 
   compressed nor deduplicated in the absence of file copying. For this 
   specific example we envision a not-deduplicatable hint. In this 
   scenario the NFS client sets the deduplication hint to advise to the 
   data reduction engine that deduplication should be enabled for the 
   file. Alternatively if a new file is being written that is not 
   based on modifying an existing file the deduplication hint is set 
   to indicate that deduplication should be disabled.

   Another use case involves compressed video files and images that 
   are written by video applications.  As such files are already 
   compressed, further attempts to compress them are likely to be 
   pointless, and may negatively impact the performance of the NFS 
   An additional scenario involves metadata at the start (header) of 
   the file; an application that did not generate the file may 
   nonetheless be able to access the metadata section in the file and 
   set the RECOMMENDED attributes file based on compression and 
   deduplication found in the file header. The NFS server doesn't 
   have visibility into metadata included in file headers and cannot 
   send file header content to the data reduction engine as separate 
   metadata. Only the user application can access and parse the header 
   and add or update the attribute value when the file is written to 
   the NFS server. 

   Additional examples of known data reduction attributes is 
   implemented in benchmarks such as SPECsfs that is using predefined 
   data reduction attributes. SPECsfs workloads [8] have DR/CR 
   (Deduplication Ratio/Compression Ratio) characteristics that were 
   collected from actual user data. They are as follows:

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        EDA                     DR/CR=50%/50%
        SWBUILD                 DR/CR=0/80%
        VDI                     DR/CR=55%/70%
        DB                      DR/CR=0/50%
        VDA                     DR/CR=0/0
        IT infrastucture        DR/CR=30%/50%
        Oracle DW               DR/CR=15%/70%
        Oracle OLTP             DR/CR=0%/65%
        Exchange 2010           DR/CR=15%/35%
        Geoseismic              DR/CR=3%/40%

   Another scenario involves placing files with the same known data 
   reduction characteristics in same directory, where the user or an 
   application sets data reduction RECOMMENDED attribute for the 
   files in a directory that are intended to apply to all files in 
   the directory and possibly also sub-directories. In this case the 
   NFS Server uses the data reduction RECOMMENDED attributes 
   of the directory to inform the data reduction engine of the data 
   reduction characteristics of blocks in all files in that directory.

3  New RECOMMENDED attributes

   RECOMMENDED attributes, [4], are a means to add new attributes 
   associated to file system objects, e.g., files and 
   directories. RECOMMENDED attributes are especially useful when 
   they add information that is not, or cannot be, present in the 
   associated object itself.    

   As RECOMMENDED attributes are stored with the file system objects 
   applications do not need to be concerned about how the attributes 
   are stored internally on the underlying file system. All major
   operating systems provide various flavors of attributes.
   Many user space tools allow RECOMMENDED attributes to be included 
   in attributes that need to be preserved when files and directories 
   are updated, moved or copied. The proposed data reduction can be 
   used by the data reduction engines in the Block Storage reduction 
   engine to increase the data reduction and server operations by 
   viewing the RECOMMENDED attributes as hints from the 
   client application regarding file compression and deduplication 
   characteristics. The Block Storage will parse these attributes and 
   change the data reduction methods according to these hints with no 
   need for the file system to know about the data reduction methods 

   RECOMMENDED attributes are intended for data needed by applications 
   rather than by an NFS client implementation. NFS implementors are 
   strongly encouraged to define the new data re4duction attributes as 
   RECOMMENDED attributes. RECOMMENDED attributes have long been 
   considered unsuitable for portability because they are inadequately 
   defined and not formally documented by any standard (such as POSIX).

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   However, evidence suggests that RECOMMENDED attributes are widely 
   deployed and their support in modern disk-based file systems is 
   fairly universal. What is different in the new usecase is that the 
   hidden metadata can be retrieved by the NFS server and
   understood by the data reduction engines of the Block Devices.
   The data reductiom RECOMMENDED attributes values can be 0 or 100 
   where 0 means "don't do this" hint and 100 is a "do this, but can't 
   predict how much reduction will actually result" hint. They can 
   also take on a percentage value, e.g., from the SPECsfs data shown 
   above. Any regular file or directory may have a set of RECOMMENDED 
   attributes, consisting of attributes Id and whose data bytes are 
   the associated attribute value [4] and data type.

   As currently specified, the NFS client or server SHOULD interpret 
   the contents of the RECOMMENDED attribute files. This document 
   proposed to add special new attributes that will be specifically 
   used for data reduction. The data reduction RECOMMENDED attributes 
   can be provided by extended attributes supported by most modern 
   file systems and can be retrieved from the local file systems on 
   the client and added to the NFS as new data reduction attributes 
   when files are exported from local file system extended attributes 
   of the files to the RECOMMENDED attributes in NFS.

4  File System Support

   In Linux, ext3, ext4, JFS, XFS, Btrfs, among other file systems
   support extended attributes. The getfattr and setfattr utilities can
   be used to retrieve and set xattrs. The names of the extended
   attributes must be prefixed by the name of the category and a dot;
   hence these categories are generally qualified as name spaces.
   In the NTFS file system, extended attributes are one of several
   supported "file streams" [5].

   RECOMMENDED attributes can be retrieved and set through system 
   calls, [6], or shell commands and generally supported by user-space 
   tools that preserve other file attributes. For example, the "rsync" 
   remote copy program will correctly preserve extended attributes 
   between Linux/ext4 and OSX/hfs by stripping off the Linux-specific 
   "user." prefix.

5  Namespaces

   Operating systems may define multiple "namespaces" in which file 
   system objects attributes can be set. Namespaces are more than 
   organizational classes; the operating system may enforce different 
   data reduction policies and allow different reduction 
   characteristics depending on the namespace. 

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   The namespace for these attributes may be file system objects 
   accessed by using the GETATTR operation. The OPEN operation returns 
   a filehandle for the file object used by the client ask for any of 
   these attributes to be returned by the client setting a bit in the 
   GETATTR request.

6  Data Reduction RECOMMENDED attributes

   RFC5661 defines RECOMMENDED attributes as opaque byte streams that 
   are associated with a directory or file and referred to by an 
   attribute Id and a value and are understood well enough to warrant 
   support in the NFSv4.1 protocol [4]. RECOMMENDED attributes are 
   intended to be used by client applications as a method to associate 
   application-specific data with a regular file or directory. We will 
   use these RECOMMENDED attributes to add New Data Reduction 
   attributes similar in concept and use to other RECOMMENDED 
   attributes. RECOMMENDED attributes are accessible to the 
   application layer using GETATTR and SETATTR and can be modified 
   by users. Note that some RECOMMENDED attributes are write-only 
   attributes, and are used in special instances of SETATTR.

   File systems typically define individual attributes using 
   GETATTR and SETATTR operations. There are no clear indications 
   on how RECOMMENDED attributes are mapped to any existing 
   recommended or optional file attributes defined in RFC5661 [2]; 
   as a result, most NFS client implementations ignore 
   application-specified RECOMMENDED attributes. This results in 
   data loss if one copies, over the NFS protocol, a file with data 
   reduction related RECOMMENDED attributes from one file system to 
   another that also supports RECOMMENDED attributes. Although 
   different data reduction engines achieve different levels of 
   reduction these attributes are used by the reduction engines to 
   increase the reduction to different levels for different algorithms. 

   While it should be possible to write guidance about how a client can 
   use the RECOMMENDED attributes mechanism to act as carving out some 
   namespace and specifying locking primitives to enforce
   atomicity constraints on individual get/set operations, this is
   problematic for data reduction attributes that are specific to 
   specific applications and file types and not defined by the user.
   As such there will be mechanisms that will detect the data 
   reduction attributes from the application or from local file 
   system xattrs [6]. The different implementations of the protocol 
   would have to address these attributes based on additional guidance
   such as reserving some portion of RECOMMENDED attribute namespace 
   for xattr-like [6] functionality.

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7  Protocol Enhancements

   This section proposes enhancements to the NFSv4 protocol operations 
   to allow data reduction RECOMMENDED attributes to be queried and 
   modified by clients. A new attribute is added to bitmap4 data type 
   to allow data reduction RECOMMENDED attributes support to be 
   queried. This follows the guidelines specified in [2] with respect 
   to minor versioning. We propose to add 2 bits that will be passed 
   to the reduction engine and used to activate/deactivate the 
   compression and/or the deduplication operations. For example 
   READDIR may be used to get a list of such attributes, and LOOKUP 
   and OPEN may select a particular attribute. Creation of a new 
   RECOMMENDED attribute may be the result of an OPEN specifying file 
   creation. Once an OPEN is done, RECOMMENDED attributes may be 
   examined and changed by normal GETATTR and SETATTR operations 
   using the filehandles and stateid returned by OPEN. The protocol 
   detailes will be provided in the next version of the draft. It is 
   RECOMMENDED that servers support arbitrary data reduction 
   attributes. A client should not depend on the ability to store any 
   RECOMMENDED attributes in the server's file system.

8.  IANA Considerations

   All IANA considerations are covered in [4].

9.  Security Considerations

   The additions to the NFS protocol for supporting data reduction 
   RECOMMENDED attributes do not alter the security considerations of 
   the NFSv4.1 protocol [4]. Data reduction hints may enable attacks 
   on Block Storage resources that support the NFS Server. Hinting at 
   more data reduction than is possible may cause excessive data 
   reduction processing, and hinting at less data reduction than is 
   possible, including hinting not to perform any data reduction, may 
   result in consumption of more potentially expensive storage 
   capacity. A future version of this draft will discuss what to do 
   about these possible resource attacks.

10.  References

10.1.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network
        File System (NFS) Version 4 Minor Version 1 External Data
        Representation Standard (XDR) Description", RFC 5662, January

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   [4]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network
        File System (NFS) Version 4 Minor Version 1 Protocol", RFC8881,
        August 2020.

10.2  Informative References

   [3]  C. Hellwig, "Using the Parallel NFS (pNFS) SCSI Layout 
        with NVMe", June 2017,
              ... nvme-00 

        "Guidelines for extended attributes".

   [6]  M. Naik, M. Eshel, "File System Extended Attributes in NFSv4" 

   [7]  ISO/IEC 14496-14 "Information technology - Coding of audio-
        visual objects - Part 14: MP4 file format"

   [8]  SPEC SFS 2014 SP2 User's Guide,


   This draft has attempted to capture the latest industry trends of
   adding data reduction attributes needed to increase efficiency of 
   newest flash NVMe technology for file servers. New protocols were
   proposed specific for NVMe media and we were inspired by new drafts 
   proposed by the editor of this draft. 

Author's Address

   Sorin Faibish
   Cirrus Data Solutions Inc.
   11 Selwyn Road
   Newton, MA  02461
   United States of America

   Phone: +1 617-510-0422

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   Philip Shilane
   Dell EMC
   228 South Street
   Hopkinton, MA 01774
   United States of America

   Phone: +1 908-286-7977

   Ivan Basov
   35 Blue Sky Drive
   Burlington, MA 01803
   United States of America

   Phone: +1 617-396-3334

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