Jim Mauro wrote:
Could be NFS synchronous semantics on file create (followed by
repeated flushing of the write cache). What kind of storage are you
using (feel free to send privately if you need to) - is it a thumper?
It's not clear why NFS-enforced synchronous semantics would induce
different behavior than the same
load to a local ZFS.
Actually i forgot he had 'zil_disable' turned on, so it won't matter in
this case.
The big difference is that the NFS server does a VOP_FSYNC on each file
create as it needs to guarantee that the changes are on stable storage.
Locally, we don't need that same guarantee so you don't have to wait
for a disk I/O to complete on each create.
eric
File creates are metadata intensive, right? And these operations need to
be synchronous to guarantee
file system consistency (yes, I am familiar with the ZFS COW model).
Anyway....I'm feeling rather naive' here, but I've seen the "NFS
enforced synchronous semantics" phrase
kicked around many times as the explanation for suboptimal performance
for metadata-intensive
operations when ZFS is the underlying file system, but I never really
understood what's "unsynchronous"
about doing the same thing to a local ZFS.
And yes, there is certainly a network latency component to the NFS
configuration, so for any
synchronous operation, I would expect things to be slower when done over
NFS.
Awaiting enlightment....
:^)
/jim
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