Yes James is right this is normal behaviour. Unless the writes are
synchronous (O_DSYNC) or explicitely flushed (fsync()) then they
are batched up, written out and committed as a transaction
every txg_time (5 seconds).
Neil.
James C. McPherson wrote:
Bob Evans wrote:
Just getting my feet wet with zfs. I set up a test system (Sunblade
1000, dual channel scsi card, disk array with 14x18GB 15K RPM SCSI
disks) and was trying to write a large file (10 GB) to the array to
see how it performed. I configured the raid using raidz.
During the write, I saw the disk access lights come on, but I noticed
a peculiar behavior. The system would write to the disk, but then
pause for a few seconds, then contineu, then pause for a few seconds.
I saw the same behavior when I made a smaller raidz using 4x36 GB
scsi drives in a different enclosure.
Since I'm new to zfs, and realize that I'm probably missing
something, I was hoping somebody might help shed some light on my
problem.
Hi Bob,
I'm pretty sure that's not a problem that you're seeing, just
ZFS' normal behaviour. Writes are coalesced as much as possible,
so the "pauses" that you observed are most likely going to be
the system waiting for suitable IOs to be gathered up and sent
out to your storage.
If you want to examine this a bit more then might I suggest the
DTrace Toolkit's iosnoop utility.
best regards,
James C. McPherson
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Neil
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