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

[Patrick Farrell]

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
________________________________
From: lustre-discuss [lustre-discuss-bounces at lists.lustre.org] on behalf of Andrew Holway [andrew.holway at gmail.com]
Sent: Tuesday, May 05, 2015 1:30 AM
To: Andrew Wagner
Cc: kevin.abbey at rutgers.edu; lustre-discuss at lists.lustre.org
Subject: Re: [lustre-discuss] zfs -- mds/mdt -- ssd model / type recommendation

ZFS should not be slower for very long. I understand that, now ZFS on Linux is stable, many significant performance problems have been identified and are being worked on.

On 5 May 2015 at 04:20, Andrew Wagner <andrew.wagner at ssec.wisc.edu<mailto:andrew.wagner at ssec.wisc.edu>> wrote:
I can offer some guidance on our experiences with ZFS Lustre MDTs. Patrick and Charlie are right - you will get less performance per $ out of ZFS MDTs vs. LDISKFS MDTs. That said, our RAID10 with 4x Dell Mixed Use Enterprise SSDs achieves similar performance to most of our LDISKFS MDTs. Our MDS was a Dell server and we wanted complete support coverage.

One of the most important things for good performance with our ZFS MDS was RAM. We doubled the amount of RAM in the system after experiencing performance issues that were clearly memory pressure related. If you expect to have tens of millions of files, I wouldn't run the MDS without at least 128GB of RAM. I would be prepared to increase that number if you run into RAM bottlenecks - we ended up going to 256GB in the end.

For a single OSS, you may not need 4x SSDs to deal with the load. We use the 4 disk RAID10 setup with a 1PB filesystem and 1.8PB filesystem. Our use case was more for archive purposes, so we wanted to go with a complete ZFS solution.



On 5/4/2015 1:18 PM, Kevin Abbey wrote:
Hi,

 For a single node OSS I'm planning to use a combined MGS/MDS. Can anyone recommend an enterprise ssd designed for this workload?  I'd like to create a raid10  with 4x ssd using zfs as the backing fs.

Are there any published/documented systems using zfs in raid 10 using ssd?

Thanks,
Kevin



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