Network File System Version 4 S. Faibish
Internet-Draft Cirrus Data Solutions Inc.
Intended status: Informational P. Shilane
Expires: December 13, 2022 Dell EMC
June 13, 2022
Support for Data Reduction Attributes in nfsv4 Version 2
draft-faibish-nfsv4-data-reduction-attributes-07
Abstract
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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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",
"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 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
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 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
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 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
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 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
used.
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
2010.
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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", RFC 8881,
August 2020.
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/
[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
Cirrus Data Solutions Inc.
11 Selwyn Road
Newton, MA 02461
United States of America
Phone: +1 617-510-0422
Email: sorin.faibish@cdsi.us.com
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Philip Shilane
Dell EMC
228 South Street
Hopkinton, MA 01774
United States of America
Phone: +1 908-286-7977
Email: philip.shilane@dell.com
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