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
> 


Reply via email to