Some comments on ZFS

Gary Jennejohn garyj at
Tue Apr 17 11:43:19 UTC 2007

Robert Watson writes:
> On Mon, 16 Apr 2007, Maxim Sobolev wrote:
> > Joerg t wrote:
> >>> There is something weird - Just ran same test again to see whether it was
> >>> a fluke - it still take 1h12 - however I saw the oppersite of Joerg. The 
> >>> "systat -vm" Freemem was permently on 2,2GB - this on a 4GB system that 
> >>> normally shows a 1,2GB - or less after a buildworld.
> >> 
> >>> hmm. Pawel are there tests that can help?
> >> 
> >> also how can we determine the real memory consumption by zfs,arc and his 
> >> vfs cache share ?
> >> 
> >> how can we precisely instrument zfs ?
> >
> > The "vmstat -m" will give you precise breakdown of kernel memory usage.
> You'll also want to use "vmstat -z".  "-m" captures memory allocated by 
> kernel malloc(9), which is used for variable-sized objects, or objects that 
> are irregularly allocated.  "-z" captures memory allocated by the kernel zone
> allocator, used for regularly sized and frequently allocated objects.  Small 
> allocations in malloc(9) are actually allocated via fixed size memory buckets
> in the zone allocator, so if looking at "-m" as well, ignore zones who's name
> s 
> consist solely of a number (i.e., "16", which is the 16-byte bucket).

Interestingly enough, I see less memory pressure since switching to ZFS.
But I'm not using RAIDZ. Previously ``make buildworld'' would use much
more memory, probably for buffer caching. It looks like ZFS doesn't use
nearly as much buffer cache as UFS (which may not be a good thing).

Gary Jennejohn / garyjATjennejohnDOTorg gjATfreebsdDOTorg garyjATdenxDOTde

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