[Lustre-discuss] Lustre requirements and tuning tricks

Joe Landman landman at scalableinformatics.com
Wed Sep 8 08:25:09 PDT 2010

Joan J. Piles wrote:

> And then 2 MDS like these:
> - 2 x Intel 5520 (quad core) processor (or equivalent).
> - 36Gb RAM.
> - 2 x 64Gb SSD disks.
> - 2 x10Gb Ethernet ports.

Hmmm ....

> After having read the documentation, it seems to be a sensible 
> configuration, specially regarding the OSS. However we are not so sure 
> about the MDS. We have seen recommendations to reserve 5% of the total 
> file system space in the MDS. Is this true and then we should go for 
> 2x2Tb SAS disks for the MDS? Is SSD really worth there?

There is a nice formula for approximating your MDS needs on the wiki. 
Basically it is something to the effect of

	Number-of-inodes-planned * 1kB = storage space required

So, for 10 million inodes, you need ~10 GB of space.  I am not sure if 
this helps, but you might be able to estimate your likely usage 
scenario.  Updating MDSes isn't easy (e.g. you have to pre-plan)

> And we have also read about having a separate storage for the OSTs' 
> journals. Is it really useful to get a pair of extra small (16Gb) SSD 
> disks for each OST to keep the journals and bitmaps?
> Finally, we have also read that it's important to have different OSTs in 
> different physical drives to avoid bottlenecks. Is thas so if we make a 
> big RAID volume and then several logical volumes (done with the hardware 
> raid card, the operating system would just see different block devices)?

Yes, though this will be suboptimal in performance.  You want traffic to 
different LUNs not sharing the same physical disks.  Build smaller RAID 
containers, and single LUNs atop those.

Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics Inc.
email: landman at scalableinformatics.com
web  : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax  : +1 866 888 3112
cell : +1 734 612 4615

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