[lustre-discuss] zfs -- mds/mdt -- ssd model / type recommendation

[Patrick Farrell]

My understanding is it's primarily ZFS rather than ZFS+Lustre, but the issue is that the Lustre MDT does a lot of IO in a manner that ZFS is not (currently) great at handling.   As I understood, the fixes will be in ZFS, not the Lustre layers above it.

Bear in mind that Lustre metdata operations are notably different from regular ZFS metadata operations.

I've copied Brian in hopes he's able to chime in - This is all second hand.

Brian - Would you mind offering a few words on this topic?
________________________________________
From: Rick Wagner [rpwagner at sdsc.edu]
Sent: Tuesday, May 05, 2015 10:07 AM
To: Wolfgang Baudler
Cc: Patrick Farrell; kevin.abbey at rutgers.edu; lustre-discuss at lists.lustre.org
Subject: Re: [lustre-discuss] zfs -- mds/mdt -- ssd model / type        recommendation

On May 5, 2015, at 7:16 AM, Wolfgang Baudler <wbaudler at gb.nrao.edu> wrote:

>> The Livermore folks leading this effort can correct me if I misspeak, but
>> they (Specifically Brian Behlendorf) presented on this topic at the
>> Developers' Day at LUG 2015 (no video of the DD talks, sorry).
>>
>>> From his discussion, the issues have been identified, but the fixes are
>>> between six months and two years away, and may still not fully close the
>>> gap.  It'll be a bit yet.
>>
>> - Patrick
>
> So, these performance issues are specific to Lustre using ZFS or is it
> problems with ZFS on Linux in general?

It's Lustre on ZFS, especially for metadata operations that create, modify, or remove inodes. Native ZFS metadata operations are much faster than what Lustre on ZFS is currently providing. That said, we've gone with a ZFS-based patchless MDS, since read operations have always been more critical for us, and our performance is more than adequate.

--Rick

>
> Wolfgang
>
>
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