Dear all
We have an HDD ceph cluster that could do with some more IOPS. One
solution we are considering is installing NVMe SSDs into the storage
nodes and using them as WAL- and/or DB devices for the Bluestore OSDs.
However, we have some questions about this and are looking for some
guidance and advice.
The first one is about the expected benefits. Before we undergo the
efforts involved in the transition, we are wondering if it is even worth
it. How much of a performance boost one can expect when adding NVMe SSDs
for WAL-devices to an HDD cluster? Plus, how much faster than that does
it get with the DB also being on SSD. Are there rule-of-thumb number of
that? Or maybe someone has done benchmarks in the past?
The second question is of more practical nature. Are there any
best-practices on how to implement this? I was thinking we won't do one
SSD per HDD - surely an NVMe SSD is plenty fast to handle the traffic
from multiple OSDs. But what is a good ratio? Do I have one NVMe SSD per
4 HDDs? Per 6 or even 8? Also, how should I chop-up the SSD, using
partitions or using LVM? Last but not least, if I have one SSD handle
WAL and DB for multiple OSDs, losing that SSD means losing multiple
OSDs. How do people deal with this risk? Is it generally deemed
acceptable or is this something people tend to mitigate and if so how?
Do I run multiple SSDs in RAID?
I do realize that for some of these, there might not be the one perfect
answer that fits all use cases. I am looking for best practices and in
general just trying to avoid any obvious mistakes.
Any advice is much appreciated.
Sincerely
Niklaus Hofer
--
stepping stone AG
Wasserwerkgasse 7
CH-3011 Bern
Telefon: +41 31 332 53 63
www.stepping-stone.ch
niklaus.hofer@xxxxxxxxxxxxxxxxx
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