> On Tue, 30 Jun 2009, Bob Friesenhahn wrote:
>
> Note that this issue does not apply at all to NFS
> service, database
> service, or any other usage which does synchronous
> writes.
I see read starvation with NFS. I was using iometer on a Windows VM, connecting
to an NFS mount on a 2008.11 physical box. iometer params: 65% read, 60%
random, 8k blocks, 32 outstanding IO requests, 1 worker, 1 target.
NFS Testing
capacity operations bandwidth
pool used avail read write read write
---------- ----- ----- ----- ----- ----- -----
data01 59.6G 20.4T 46 24 757K 3.09M
data01 59.6G 20.4T 39 24 593K 3.09M
data01 59.6G 20.4T 45 25 687K 3.22M
data01 59.6G 20.4T 45 23 683K 2.97M
data01 59.6G 20.4T 33 23 492K 2.97M
data01 59.6G 20.4T 16 41 214K 1.71M
data01 59.6G 20.4T 3 2.36K 53.4K 30.4M
data01 59.6G 20.4T 1 2.23K 20.3K 29.2M
data01 59.6G 20.4T 0 2.24K 30.2K 28.9M
data01 59.6G 20.4T 0 1.93K 30.2K 25.1M
data01 59.6G 20.4T 0 2.22K 0 28.4M
data01 59.7G 20.4T 21 295 317K 4.48M
data01 59.7G 20.4T 32 12 495K 1.61M
data01 59.7G 20.4T 35 25 515K 3.22M
data01 59.7G 20.4T 36 11 522K 1.49M
data01 59.7G 20.4T 33 24 508K 3.09M
data01 59.7G 20.4T 35 23 536K 2.97M
data01 59.7G 20.4T 32 23 483K 2.97M
data01 59.7G 20.4T 37 37 538K 4.70M
While writes are being committed to the ZIL all the time, periodic dumping to
the pool still occurs, and during those times reads are starved. Maybe this
doesn't happen in the 'real world' ?
-Scott
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