[lustre-discuss] Tuning for metadata performance

Tue Jan 5 10:51:12 PST 2021

Probably the best single thing you could do for metadata performance
would be to switch to SSD, or better NVMe, storage.  ZFS is very sync
and IOPS hungry, so using HDDs is killer for ZFS metadata performance.

If you want to minimize the downtime, you could incrementally replace the
HDDs in the zpool with larger SSD devices and resilver between each
one.  I recall LLNL doing this in the first months of their first ZFS-based
Lustre filesystem for this reason.

Going to NVMe-based devices is even better for IOPS/bandwidth, but
can't be done completely live.  You could potentially use repeated zfs
send/recv to get an almost uptodate copy on a new MDS, then take a small
outage to do the final resync. However, I've also seen reports that send/recv is painfully slow with HDD MDTs so you should probably test that before committing to a solution.

Cheers, Andreas

On Jan 5, 2021, at 08:47, Vicker, Darby J. (JSC-EG111)[Jacobs Technology, Inc.] <darby.vicker-1 at nasa.gov> wrote:

Hello,

I'm looking for some advice on tuning our existing lustre file system to achieve better metadata performance.  This file system is getting fairly old – its been in production for almost 4 years now.  The hardware and our existing tuning efforts can be found here.

http://lists.lustre.org/pipermail/lustre-discuss-lustre.org/2017-April/014390.html

The hardware is the same but we have upgraded the software stack a few times – now on CentOS 7.6, ZFS 0.7.9 and lustre 2.10.8.  We do plan to upgrade to the latest CentOS 7.x and either lustre 2.12 or 2.13 soon.  The MDS hardware isn't well-described in that thread so here are more details:

Chassis: Supermicro 2U Twin Server
Processor: 4 x QuadCore Xeon Processor E52637 v2 3.50GHz (2 sockets/8 cores per node)
Memory: 16 x 16GB PC314900 1866MHz DDR3 ECC Registered DIMM (128GB per node)

External JBOD:
Chassis: 24x HotSwap 2.5" SAS  12Gb/s SAS Dual Expander
Drives: 12 x 600GB SAS 3.0 12.0Gb/s 15000RPM  2.5"  Seagate Enterprise Performance 15K HDD (512n)
Controller Card: LSI SAS 9300-8e SAS 12Gb/s PCIe 3.0 8-Port Host Bus Adapter

The above hardware and tuning served us well for a long time but the lab has grown, both in number of lustre clients (now up to ~200 ethernet clients and ~500 IB clients) and the number of users in the lab.  With the extra users have come different types of workloads.  Peviously, the file system was most used for workloads with a fairly small number of large files.  We now see workloads that include 100's of concurrent processes all doing mixed small and large file IO on a lot of files (e.g. each process clones a repo, compiles a code and runs a serial sim that writes a lot of data).

I recently ran the io500 tests and our LFS stats for MDEasy and MDHard are pretty bad, even when compared to the lowest MD stats on the current io500 list.  Our standard NFS server handily beats our LFS wrt MD performance.  So I'm hopeful that we can squeeze more MD performance out of our LFS.  Obviously, software tuning on the existing hardware would be preferred but we are open to hardware additions/upgrades if that would help (e.g. adding more MDS's).  There are a lot of tuning options in both ZFS and lustre so I'm hoping someone can point me in the right direction.  Are DNE and/or DoM expected to help?  I attended the SC20 Lustre BoF and it sounds like 2.13 has some metadata performance improvements, so just an upgrade might help.  We have dual MDS's now but for HA, not performance.  I'd hate to lose the HA aspect as we utilize it for failover quite a bit (maintenance, etc.) but it would probably be worth it if MD performance was significantly improved.  If I understand correctly, there is some overhead with DNE and performance suffers with just two MDS's with a benefit with 4 or more MDS's, correct?  So that wouldn't be a good option for us unless we add MDS's?  Would an upgrade to SSD or NVMe in our MDTs help?

I would greatly appreciate thoughts on the best path forward for making improvements.

Thanks,
Darby
_______________________________________________
lustre-discuss mailing list
lustre-discuss at lists.lustre.org
http://lists.lustre.org/listinfo.cgi/lustre-discuss-lustre.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.lustre.org/pipermail/lustre-discuss-lustre.org/attachments/20210105/90344ea5/attachment.html>