[zfs-discuss] High Resource Usage During Copy

Robin Humble robin.humble+zfs at anu.edu.au
Sun Jun 12 10:34:26 EDT 2011


On Sun, Jun 12, 2011 at 01:29:20PM +0000, Steve Costaras wrote:
>As for memory usage, yes that's normal for ZFS as to avoid fragmentation it will buffer all writes and flush to disk when memory pressure is great enough or when a file is closed. This can also skew performance benchmarks when you have a lot of memory.

speaking of benchmarks - I'm trying to run tests with Lustre on ZFS,
and I'm seeing higher than expected read rates in some cases.

is there a way to drop the ZFS ARC to make sure I'm reading from disk
instead of ram?

the benchmark tests I'm running are small and fast, unlike real
production loads. Lustre also does its own read and write-through
caching, so I want eliminate the ZFS ram variable.

I'm doing a Linux standard 'echo 3 > /proc/sys/vm/drop_caches'
everywhere before reads, but I don't know if zfs and/or spl are hanging
onto ram caches under the hood... ??

cheers,
robin



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