--As of April 9, 2011 9:27:41 PM -0700, Chris Telting is alleged to have
said:
Does ZFS in any way do performance testing of read/right operating in
light of where the data is stored on the drive? i.e. the outside sectors
of hard drives perform faster. If it does do read/write location testing
can it be shut off or does it detect SSDs? What about tracing
application sector reading and reordering sectors so that they follow one
another according to typical usage? i.e. the sectors are already in the
linear read ahead buffer?
--As for the rest, it is mine.
I'll let you see Dan Nelson's answer for the striping questions. While I
have no inside knowledge of the performance testing handling of ZFS, it
doesn't appear to do anything too automagically in that arena. You give it
a drive, it will use it, like any other file system. It can give you stats
on I/O for each drive as well as the pool in general, and it appears to try
to balance reads/writes across all the drives, but that's implied in
mirroring or RAID setups. (And remember: ZFS can do either one. You can't
add to a RAID volume though, like you can to a mirrored volume.)
It does try to cache files, in a fairly aggressive fashion. (By the docs,
ZFS will try to fill *all unused RAM* with cached files by default.) And
while it doesn't appear to have anything that auto-detects faster drives,
you can specify a drive for caching or for the write log. (Caching speeds
up reads, and deduplication in versions that support that. The write log
speeds up writes.) Telling it to use a SSD for that will speed up those
operations considerably. (Note that while a cache drive is considered
expendable, the write-log drive is not, and it's recommended that you set
up a mirror for it.)
Daniel T. Staal
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