The (sorry?) state of pNFS documentation?! Abandonware?

The (sorry?) state of pNFS documentation?! Abandonware?

[Martin Wege]

Hello!

Is there any up to date documentation for pNFS server support in the
Linux 6.6 kernel?

For example: https://wiki.linux-nfs.org/wiki/index.php/PNFS_Development_Git_tree
says "THIS IS OUT OF DATE. The particular pnfs code described here is
no longer under development.", which sounds like pNFS support in Linux
is abandonware.

Thanks,
Martin

Re: The (sorry?) state of pNFS documentation?! Abandonware?

[Chuck Lever]

On 2/11/25 7:54 AM, Martin Wege wrote:
> Is there any up to date documentation for pNFS server support in the
> Linux 6.6 kernel?

There isn't up-to-date documentation for NFSD's pNFS support. There are
various efforts going on to improve it, but as we are swamped with other
more pressing issues, there hasn't been good progress.

pNFS block is supported, but it's not straightforward to set up.

pNFS flexfiles is supported, but the implementation supports only the
case where the DS and MDS are the same server.

NFSD does not implement the other layout types.


-- 
Chuck Lever

Re: The (sorry?) state of pNFS documentation?! Abandonware?

[Martin Wege]

On Tue, Feb 11, 2025 at 3:00 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>
> On 2/11/25 7:54 AM, Martin Wege wrote:
> > Is there any up to date documentation for pNFS server support in the
> > Linux 6.6 kernel?
>
> There isn't up-to-date documentation for NFSD's pNFS support. There are
> various efforts going on to improve it, but as we are swamped with other
> more pressing issues, there hasn't been good progress.
>
> pNFS block is supported, but it's not straightforward to set up.
>
> pNFS flexfiles is supported, but the implementation supports only the
> case where the DS and MDS are the same server.
>
> NFSD does not implement the other layout types.

More questions:
1. Clarification, please:
Which layout types are and are not supported:
LAYOUT4_NFSV4_1_FILES
LAYOUT4_OSD2_OBJECTS
LAYOUT4_BLOCK_VOLUME

2. Is Flexfiles also part of enum layouttype4, or something different?

3. dCache supports pNFS MetaDataServer (MDS), and NFSv3 Data Servers
(DS). Where is the spec for this? And why, WHY NFSv3 DS? Why not
NFSv4.1 DS=

Thanks,
Martin

Re: The (sorry?) state of pNFS documentation?! Abandonware?

[Chuck Lever]

On 3/26/25 10:33 AM, Martin Wege wrote:
> On Tue, Feb 11, 2025 at 3:00 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>>
>> On 2/11/25 7:54 AM, Martin Wege wrote:
>>> Is there any up to date documentation for pNFS server support in the
>>> Linux 6.6 kernel?
>>
>> There isn't up-to-date documentation for NFSD's pNFS support. There are
>> various efforts going on to improve it, but as we are swamped with other
>> more pressing issues, there hasn't been good progress.
>>
>> pNFS block is supported, but it's not straightforward to set up.
>>
>> pNFS flexfiles is supported, but the implementation supports only the
>> case where the DS and MDS are the same server.
>>
>> NFSD does not implement the other layout types.
> 
> More questions:
> 1. Clarification, please:
> Which layout types are and are not supported:
> LAYOUT4_NFSV4_1_FILES
> LAYOUT4_OSD2_OBJECTS
> LAYOUT4_BLOCK_VOLUME

As I stated above, pNFS block is implemented. "Does not implement the
other layout types" means the NFSV4_1_FILES and OSD2_OBJECTS layout
types are not implemented.

The I/O protocols that pNFS block can use include SCSI, iSCSI, and NVMe.


> 2. Is Flexfiles also part of enum layouttype4, or something different?

Flexfiles is a layout type. It is described in RFC 8435

  https://datatracker.ietf.org/doc/html/rfc8435

NFSD's implementation is simplified and not for production use. It is
useful for testing client implementations of the flexfile layout type
and not much more at this time.


> 3. dCache supports pNFS MetaDataServer (MDS), and NFSv3 Data Servers
> (DS). Where is the spec for this?

This sounds like the flexfiles layout type to me. You will have to
confirm that with Tigran and his team.


> And why, WHY NFSv3 DS? Why not NFSv4.1 DS=

Supporting NFSv4.1 data servers is what the RFC 5661 NFSV4_1_FILES
layout type already does.

For more on the motivation behind flexfiles, consult RFC 8435. But
generally the reasons are:

- NFSv3 READ and WRITE continue to be lower latency than NFSv4

- There's still a lot of data in the world that lives on NFSv3-only
servers. Serving it in place is cheaper than migrating it.


-- 
Chuck Lever

Re: The (sorry?) state of pNFS documentation?! Abandonware?

[Tigran Mkrtchyan]

On March 26, 2025 3:33:19 PM GMT+01:00, Martin Wege <martin.l.wege@gmail.com> wrote:
>On Tue, Feb 11, 2025 at 3:00 PM Chuck Lever <chuck.lever@oracle.com> wrote:
>>
>> On 2/11/25 7:54 AM, Martin Wege wrote:
>> > Is there any up to date documentation for pNFS server support in the
>> > Linux 6.6 kernel?
>>
>> There isn't up-to-date documentation for NFSD's pNFS support. There are
>> various efforts going on to improve it, but as we are swamped with other
>> more pressing issues, there hasn't been good progress.
>>
>> pNFS block is supported, but it's not straightforward to set up.
>>
>> pNFS flexfiles is supported, but the implementation supports only the
>> case where the DS and MDS are the same server.
>>
>> NFSD does not implement the other layout types.
>
>More questions:
>1. Clarification, please:
>Which layout types are and are not supported:
>LAYOUT4_NFSV4_1_FILES
>LAYOUT4_OSD2_OBJECTS
>LAYOUT4_BLOCK_VOLUME
>
>2. Is Flexfiles also part of enum layouttype4, or something different?
>
>3. dCache supports pNFS MetaDataServer (MDS), and NFSv3 Data Servers
>(DS). Where is the spec for this? And why, WHY NFSv3 DS? Why not
>NFSv4.1 DS=
>

dCache supports nfsv41_files (rfc 5661) and flexfiles with tightly coupled nfsv4.1 DSes (rfc8435). 

Tigran. 


>Thanks,
>Martin
>