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RE: [Linux-cluster] GFS performance



Hi Wendy,

Thanks for looking into this, and for your preliminary feedback.

I am surprised that handling locking for 8 files might cause major performance degradation with GFS versus iSCSI-direct. As for latency, all the devices are directly connected to a Cisco 3560G switch and on the same VLAN, so I expect Ethernet/layer-2 latencies to be sub-millisecond.  Also, note that the much faster iSCSI performance was on the same GbE connections between the same devices and systems, so network throughput and latency are the same.

GFS overhead, in handling locking (most likely) and any GFS filesystem overhead are the likely causes IMO.

Looking forward to any analysis and guidance you may be able to provide on getting GFS performance closer to iSCSI-direct.

- K



-----Original Message-----

Intuitively (by reading your iozone command), this is a locking issue.
There are lots to say on your setup, mostly because all data and lock
traffic are funneling thru the same network. Remember locking is mostly
to do with *latency*, not bandwidth. So even your network is not
saturated, the performance can go down. It is different from the rsync
issue (as described by Jos Vos) so the glock trimming patch is not
helpful in this case.

However, I won't know for sure until we get the data analyzed. Thanks
for the input.

-- Wendy



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