Support for Data Reduction Attributes in nfsv4 Version 2
draft-faibish-nfsv4-data-reduction-attributes-02

Network File System Version 4                                 S. Faibish
Internet-Draft                                                  D. Black
Intended status: Informational                                P. Shilane
Expires: June 24, 2020                                          Dell EMC
                                                       December 24, 2019
                          

    Support for Data Reduction Attributes in nfsv4 Version 2
        draft-faibish-nfsv4-data-reduction-attributes-02

Abstract

   This document proposes extending NFSv4 operations to add new 
   named 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 named 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.       

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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3. New Named Attributes  . . . . . . . . . . . . . . . . . . . .   8
   4. File System Support . . . . . . . . . . . . . . . . . . . . .   9
   5. Namespaces  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   6. Data Reduction Named Attributes . . . . . . . . . . . . . . .   9
   7. Protocol Enhancements . . . . . . . . . . . . . . . . . . . .  10
   8. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . .  11
        10.1.  Normative References . . . . . . . . . . . . . . . .  11
        10.2  Informative References . . . . . . . . . . . . . . . . 11
   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 named 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 name 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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   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 named 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 named attributes as metadata directly to the 
   Reduction Engine via an extension to the interface to Block Storage.

   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 named attributes.

   So, although the attributes are stored with the files, the current 
   NFSv4 named 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 named attributes and 
   whose data bytes are the value of the attribute. If the NFS 
   server extracts the data reduction named 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 filehandle for the named attributes is a directory object 
   accessible by LOOKUP or READDIR and contains files whose names 
   represent the named attributes and whose data bytes are the value 
   of the attribute. 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 deduplication.

   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 named 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 named 
   attributes in hidden directories of attributes associated with 
   each file and directory.    
    
   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 named 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. The pNFS 
   client passes that information via a hidden named attribute that 
   hints that the file is compressible. The pNFS server will change 
   or add a new data reduction named attribute and will transmit the 
   data bytes, that are the value of the named 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 named attribute data bytes are changed 
   to indicate that the data has been compressed, the compression 
   engine does not compress the incoming blocks.

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   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 
   Server. 
  
   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 named 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:

        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 named attribute in the directory of 
   attributes associated with the 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 named attributes 
   of the directory to inform the data reduction engine of the data 
   reduction characteristics of blocks in all files in that directory.

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3  New Named Attributes

   Named attributes, [4], are a means to associate a hidden directory 
   of attributes with file system objects, e.g., files and 
   directories. Named attributes are especially useful when they 
   add information that is not, or cannot be, present in the 
   associated object itself. User-space applications can arbitrarily 
   create, read from, and write new attributes of a file in that 
   directory.   

   As named attributes are stored in a hidden directory
   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 named attributes.
   Many user space tools allow named attributes to be included in 
   attributes that need to be preserved when files and directories are 
   updated, moved or copied. The filehandle for named attributes is a 
   directory object accessible by LOOKUP or READDIR and contains files 
   whose names represent the named attributes and whose data bytes are 
   the value of the attribute.

   The proposed data reduction attributes are opaque to the file 
   system but 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 named 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 
   used.

   Named 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. Named attributes have long been considered 
   unsuitable for portability because they are inadequately defined 
   and not formally documented by any standard (such as POSIX). 
   However, evidence suggests that named 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 named attributes 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 named attributes, 
   consisting of a hidden file whose names represent the named
   attributes and whose data bytes are the value of the associated 
   attribute value [4].

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   As currently specified, the NFS client or server SHOULD interpret 
   the contents of the named attribute files. This document proposed 
   to add special named attributes that will be specifically used for 
   data reduction. The data reduction named 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 new named attributes when files are exported from 
   local file system extended attributes of the files to the named 
   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].

   Named 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 named 
   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. The namespace for these attributes may be 
   accessed by using the OPENATTR operation. The OPENATTR operation
   returns a filehandle for a virtual "named attribute directory", 
   and further perusal and modification of the namespace may be done 
   using operations that work on more typical directories.

6  Data Reduction Named Attributes

   RFC5661 defines named attributes as opaque byte streams that are
   associated with a directory or file and referred to by a string name
   [4]. Named 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 named attributes directories 
   to add New Data Reduction attributes similar in concept and 
   use to other named attributes, but there are subtle differences. 

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   Named attributes are accessed by NFSv4 OPENATTR operation, which
   accesses a hidden directory of attributes associated with a file
   system object. Named attributes are accessible to the 
   application layer using GETATTR and OPENATTR and can be modified 
   by users. File systems typically define individual named attributes
   using named attributes GETATTR and SETATTR operations. Named 
   attributes generally have size limits ranging from a few bytes to 
   several kilobytes; the maximum supported size is not universally 
   defined and is usually restricted by the file system.

   There are no clear indications on how named attributes are mapped to
   any existing recommended or optional file attributes defined in RFC 
   5661 [2]; as a result, most NFS client implementations ignore 
   application-specified named attributes. This results in data loss 
   if one copies, over the NFS protocol, a file with data reduction 
   related named attributes from one file system to another that also 
   supports named 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 named 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 named attribute namespace for xattr-like [6] 
   functionality.

7  Protocol Enhancements

   This section proposes enhancements to the NFSv4 protocol operations 
   to allow data reduction named attributes to be queried and modified
   by clients. A new attribute is added to bitmap4 data type to allow 
   data reduction named 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 named attributes, and LOOKUP and OPEN may select a 
   particular attribute. Creation of a new named attribute may be the 
   result of an OPEN specifying file creation. Once an OPEN is done, 
   named attributes may be examined and changed by normal READ and 
   WRITE operations using the filehandles and stateid returned by OPEN.

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   The protocol detailes will be provided in the next version of the 
   draft. It is RECOMMENDED that servers support arbitrary named 
   attributes. A client should not depend on the ability to store any 
   named 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 
   named 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
        2010.

   [4]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network
        File System (NFS) Version 4 Minor Version 1 Protocol", RFC 5661,
        January 2010.

10.2  Informative References

   [3]  C. Hellwig, "Using the Parallel NFS (pNFS) SCSI Layout 
        with NVMe", June 2017, 
        https://tools.ietf.org/html/draft-hellwig-nfsv4-scsi-layout-
              ... nvme-00 

   [5]  http://www.freedesktop.org/wiki/CommonExtendedAttributes,
        "Guidelines for extended attributes".

   [6]  M. Naik, M. Eshel, "File System Extended Attributes in NFSv4"
        https://datatracker.ietf.org/doc/rfc8276/ 

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   [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, 
        http://spec.org/sfs2014/docs/usersguide.pdf

Acknowledgments

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

   Phone: +1 508-249-5745
   Email: faibish.sorin@dell.com

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

   Phone: +1 908-286-7977
   Email: philip.shilane@dell.com

   David Black
   DellEMC 
   176 South Street
   Hopkinton, MA  01748
   United States of America

   Phone: +1 774-350-9323
   Email: david.black@dell.com

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