On 01/22/2013 01:59 PM, martin wrote:
Hi list,
In a mixed SSD & SATA setup (5 or 8 nodes each holding 8x SATA and 4x
SSD) would it make sense to skip having journals on SSD or is the
advantage of doing so just too great? We're looking into having 2 pools,
sata and ssd and will be creating guests belonging into either of these
groups based on if they require high/heavy io.
Also, we currently lean on going with a very simple setup using a
serverboard with 8x onboard raid slots (LSI 2308) and 6x onboard sata
slots and just attach all disks to both onboard controller and onboard
slots (for cost and simplicity) - and just pass them along as JBOD.
Any suggestions/input about:
- Would it make sense to drop onboard controller and aim for a better
controller (cache/battery backed 12-16 port one)
- Attach another cheapo JBOD card like SAS2008/LSI 2308 etc.
- or just go with this setup (to keep it simpler and cheaper)
You may be interested in reading some of our past performance articles:
http://ceph.com/community/ceph-performance-part-1-disk-controller-write-throughput/
http://ceph.com/community/ceph-performance-part-2-write-throughput-without-ssd-journals/
http://ceph.com/uncategorized/argonaut-vs-bobtail-performance-preview/
We didn't test the on-board controller on the supermicro MB, but those
will at least give you some idea of what different controllers can do
with and without SSDs.
Journals:
- Would it make sense to kill say 1 ssd and 1 sata and attach 2 fast SSD
for journals? Or would that be 'redundant' in our case since we already
have a pool with sata and ssd (we do not expect heavy io in the sata pool)
Rbd striping:
- Performance - afaik rbd is striped over objects; if one would create
say a 20GB rbd image would this mostly be striped over very few
objects/pg (say ~3 nodes as would be min. in our setup) or would one
expect it to be striped over pretty much the entirety of the nodes (5 or
8 in our case) in smaller objects (or even across all OSD?)
Disks:
- Any advice for SATA disks? I know a vendor like Seagate have their
'normal' enterprise disks (ES.3-models) and are also selling their
cloud-based disks (CS models). Any suggestions/experience what to look
at/aim at? Or what are people using in general?
I've been using 1TB Seagate Constellation Enterprise SATA drives for
testing and have had mostly good luck (1 or 2 duds out of 36) with no
failures. Long term experience for me is that all vendors seem to have
bad batches here and there.
Disk utilization:
- I've noticed in our testsetup that we have several pg's taking up
>300GB data each - is this normal? This results in some odd situations
where disk usage can vary by up to 15-20% (2TB disks). If we adjust the
weight it eventually means one of these pg will go to another disk and
it has to copy 300GB data. We're using 0.56.1.
Some output from 'ceph pg dump':
pg_stat objects mip degr unf bytes log disklog state
state_stamp v reported up acting last_scrub
scrub_stamp last_deep_scrub deep_scrub_stamp
4.5 90772 0 0 0 379301388412 150969 150969
active+clean 2013-01-22 00:07:13.384272 2827'412414
2795'3317565 [1,2] [1,2] 2827'397587 2013-01-22
00:07:13.384225 2744'299767 2013-01-17 05:40:40.737279
Results in disk usage like:
Filesystem Size Used Avail
Use% Mounted on
/dev/sdd1 1.9T 1.4T 446G
77% /srv/ceph/osd5
/dev/sdb1 1.4T 1.1T 331G
77% /srv/ceph/osd0
/dev/sda1 1.9T 1.4T 442G
77% /srv/ceph/osd1
/dev/sdc1 1.9T 1.8T 84G
96% /srv/ceph/osd2
If we reweight sdc down (even with 0.00X % at a time) one of those big
pg's will eventually move to any one of the above disks and the image
will look exactly the same with the exception another disk will have 96%
usage instead (I've bumped cluster full % to 98% in this setup).
It may (or may not) help to use a power-of-2 number of PGs. It's
generally a good idea to do this anyway, so if you haven't set up your
production cluster yet, you may want to play around with this.
Basically just take whatever number you were planning on using and round
it up (or down slightly). IE if you were going to use 7,000 PGs, round
up to 8192.
Mark
Apologies up front if questions like these are not supposed to go to
this mailling-list.
Any advice/ideas/suggestions are very welcome!
Cheers,
Martin Nielsen
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