* osd max write size
@ 2013-01-20 19:06 Stefan Priebe
2013-01-20 22:20 ` Gregory Farnum
0 siblings, 1 reply; 2+ messages in thread
From: Stefan Priebe @ 2013-01-20 19:06 UTC (permalink / raw)
To: ceph-devel@vger.kernel.org
Hi,
what is the purpose or idea behind this setting?
Greets,
Stefan
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: osd max write size
2013-01-20 19:06 osd max write size Stefan Priebe
@ 2013-01-20 22:20 ` Gregory Farnum
0 siblings, 0 replies; 2+ messages in thread
From: Gregory Farnum @ 2013-01-20 22:20 UTC (permalink / raw)
To: Stefan Priebe; +Cc: ceph-devel@vger.kernel.org
On Sunday, January 20, 2013 at 11:06 AM, Stefan Priebe wrote:
> Hi,
>
> what is the purpose or idea behind this setting?
>
Couple different things:
1) The OSDs can't accept writes which won't fit inside their journal, and if you have a small journal you could conceivably attempt to write something which wouldn't fit. This doesn't happen so much any more, but it did sometimes in the past.
1b) The MDS uses this setting to limit the size of some of its operations (mostly directory updates), which can (rarely) grow quite large.
2) The OSDs don't have any other strict limits on how large an op you send around, but performance becomes a problem if they grow too large. This setting caps the operation size it allows.
It defaults to 90MB and you can change it if you want to, but I'm not sure why you would…
-Greg
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