If using storcli/perccli for manipulating the LSI controller, you can disable the on-disk
write cache with:
storcli /cx/vx set pdcache=off
You can also ensure that you turn off write caching at the controller level with
storcli /cx/vx set iopolicy=direct
storcli /cx/vx set wrcache=wt
You can also tweak the readahead value for the vd if you want, though with an ssd, I
don't think it will be much of an issue.
storcli /cx/vx set rdcache=nora
I'm sure the megacli alternatives are available with some quick searches.
May also want to check your c-states and p-states to make sure there isn't any
aggressive power saving features getting in the way.
Reed
On Aug 31, 2020, at 7:44 AM, VELARTIS Philipp
Dürhammer <p.duerhammer(a)velartis.at> wrote:
We have older LSi Raid controller with no HBA/JBOD option. So we expose the single disks
as raid0 devices. Ceph should not be aware of cache status?
But digging deeper in to it it seems that 1 out of 4 serves is performing a lot better
and has super low commit/applay rates while the other have a lot mor (20+) on heavy
writes. This just applys fore the ssd. For the hdds I cant see a difference...
-----Ursprüngliche Nachricht-----
Von: Frank Schilder <frans(a)dtu.dk>
Gesendet: Montag, 31. August 2020 13:19
An: VELARTIS Philipp Dürhammer <p.duerhammer(a)velartis.at>at>;
'ceph-users(a)ceph.io' <ceph-users(a)ceph.io>
Betreff: Re: Can 16 server grade ssd's be slower then 60 hdds? (no extra journals)
Yes, they can - if volatile write cache is not disabled. There are many threads on this,
also recent. Search for "disable write cache" and/or "disable volatile
write cache".
You will also find different methods of doing this automatically.
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
________________________________________
From: VELARTIS Philipp Dürhammer <p.duerhammer(a)velartis.at>
Sent: 31 August 2020 13:02:45
To: 'ceph-users(a)ceph.io'
Subject: [ceph-users] Can 16 server grade ssd's be slower then 60 hdds? (no extra
journals)
I have a productive 60 osd's cluster. No extra Journals. Its performing okay. Now I
added an extra ssd Pool with 16 Micron 5100 MAX. And the performance is little slower or
equal to the 60 hdd pool. 4K random as also sequential reads. All on dedicated 2 times 10G
Network. HDDS are still on filestore. SSD on bluestore. Ceph Luminous.
What should be possible 16 ssd's vs. 60 hhd's no extra journals?
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