zfs very poor performance compared to ufs due to lack of cache?

[Andriy Gapon]

[ping]

on 21/09/2010 17:23 Andriy Gapon said the following:
> on 21/09/2010 16:53 Steven Hartland said the following:
>> That's what I thought you where saying. Is there a test you would suggest to confirm
>> either way more accurately?
> 
> Perhaps you can try the test scenario that you described and monitor parameters
> suggested by Wiktor in this thread.
> 
> That is, have two large files and set arc max size such that one of them can fit
> in ARC readily, but two of them won't fit by a large margin.  Make sure that
> remaining RAM is large enough to hold both files in page cache.
> 
> 1. sendfile one file, then the other
> 2. record kstat.zfs.misc.arcstats values
> 3. sendfile the first file again
> 4. record kstat.zfs.misc.arcstats values
> 
> If the first file data was re-used from page cache, then you won't see much
> changes in kstat.zfs.misc.arcstats.  If it had to be taken from ARC or from disk,
> then either ARC hits or ARC misses will grow noticeably.
> 
> Make sure to not have any parallel activity that could affect kstat.zfs.misc.arcstats.
> 
> I think kstat.zfs.misc.arcstats.hits and kstat.zfs.misc.arcstats.misses are two
> primary indicators in this test.
> 


-- 
Andriy Gapon