<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto">Hi Kevin, <div>as you already pointed out, having a RAID stripe size (or a multiple of it) not matching GPFS blocksize, is a bad idea. Every write would cause a read-modify-write operation to keep the parity.</div><div>So for data LUNs RAID5 with 4+P or 8+P is fully ok.</div><div>For metadata, if you are keen on performance, I would stay with RAID1, or even RAID0, so you aren’t affected by possible RAID rebuild performance drops.<br> <br><div>Regards, Achim</div><div><br></div><div><br>Am 05.09.2018 um 17:35 schrieb Buterbaugh, Kevin L <<a href="mailto:Kevin.Buterbaugh@Vanderbilt.Edu">Kevin.Buterbaugh@Vanderbilt.Edu</a>>:<br><br></div><blockquote type="cite"><div>
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Hi All,
<div class=""><br class=""></div><div class="">We are in the process of finalizing the purchase of some new storage arrays (so no sales people who might be monitoring this list need contact me) to life-cycle some older hardware. One of the things we are considering is the purchase of some
new SSD’s for our “/home” filesystem and I have a question or two related to that.</div><div class=""><br class=""></div><div class="">Currently, the existing home filesystem has it’s metadata on SSD’s … two RAID 1 mirrors and metadata replication set to two. However, the filesystem itself is old enough that it uses 512 byte inodes. We have analyzed our users files and know
that if we create a new filesystem with 4K inodes that a very significant portion of the files would now have their _data_ stored in the inode as well due to the files being 3.5K or smaller (currently all data is on spinning HD RAID 1 mirrors).</div><div class=""><br class=""></div><div class="">Of course, if we increase the size of the inodes by a factor of 8 then we also need 8 times as much space to store those inodes. Given that Enterprise class SSDs are still very expensive and our budget is not unlimited, we’re trying to get the
best bang for the buck.</div><div class=""><br class=""></div><div class="">We have always - even back in the day when our metadata was on spinning disk and not SSD - used RAID 1 mirrors and metadata replication of two. However, we are wondering if it might be possible to switch to RAID 5? Specifically, what we are
considering doing is buying 8 new SSDs and creating two 3+1P RAID 5 LUNs (metadata replication would stay at two). That would give us 50% more usable space than if we configured those same 8 drives as four RAID 1 mirrors.</div><div class=""><br class=""></div><div class="">Unfortunately, unless I’m misunderstanding something, mean that the RAID stripe size and the GPFS block size could not match. Therefore, even though we don’t need the space, would we be much better off to buy 10 SSDs and create two 4+1P RAID
5 LUNs?</div><div class=""><br class=""></div><div class="">I’ve searched the mailing list archives and scanned the DeveloperWorks wiki and even glanced at the GPFS documentation and haven’t found anything that says “bad idea, Kevin”… ;-)</div><div class=""><br class=""></div><div class="">Expanding on this further … if we just present those two RAID 5 LUNs to GPFS as NSDs then we can only have two NSD servers as primary for them. So another thing we’re considering is to take those RAID 5 LUNs and further sub-divide them into a
total of 8 logical volumes, each of which could be a GPFS NSD and therefore would allow us to have each of our 8 NSD servers be primary for one of them. Even worse idea?!? Good idea?</div><div class=""><br class=""></div><div class="">Anybody have any better ideas??? ;-)</div><div class=""><br class=""></div><div class="">Oh, and currently we’re on GPFS 4.2.3-10, but are also planning on moving to GPFS 5.0.1-x before creating the new filesystem.</div><div class=""><br class=""></div><div class="">Thanks much…</div><div class=""><br class=""></div><div class=""><div class=""><div class="">—</div><div class="">Kevin Buterbaugh - Senior System Administrator</div><div class="">Vanderbilt University - Advanced Computing Center for Research and Education</div><div class=""><a href="mailto:Kevin.Buterbaugh@vanderbilt.edu" class="">Kevin.Buterbaugh@vanderbilt.edu</a> - (615)875-9633</div><div class=""><br class=""></div><br class="Apple-interchange-newline"></div><br class=""></div>
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