Re: MDS cache size limits

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On Mon, Jan 8, 2018 at 8:02 PM, Marc Roos <M.Roos@xxxxxxxxxxxxxxxxx> wrote:
>
> I guess the mds cache holds files, attributes etc but how many files
> will the default "mds_cache_memory_limit": "1073741824" hold?

We always used to get asked how much memory a given mds_cache_size (in
inodes) would require, I guess it was only a matter of time until the
reverse question was asked :-)

John

>
>
> -----Original Message-----
> From: Stefan Kooman [mailto:stefan@xxxxxx]
> Sent: vrijdag 5 januari 2018 12:54
> To: Patrick Donnelly
> Cc: Ceph Users
> Subject: Re:  MDS cache size limits
>
> Quoting Patrick Donnelly (pdonnell@xxxxxxxxxx):
>>
>> It's expected but not desired: http://tracker.ceph.com/issues/21402
>>
>> The memory usage tracking is off by a constant factor. I'd suggest
>> just lowering the limit so it's about where it should be for your
>> system.
>
> Thanks for the info. Yeah, we did exactly that (observe and adjust
> setting accordingly). Is this something worth mentioning in the
> documentation? Escpecially when this "factor" is a constant? Over time
> (with issue 21402 being worked on) things will change. Ceph operators
> will want to make use of as much cache as possible without
> overcommitting (MDS won't notice until there is no more memory left,
> restart, and looses all its cache :/).
>
> Gr. Stefan
>
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