[gpfsug-discuss] Write performances and filesystem size
Ivano Talamo
Ivano.Talamo at psi.ch
Wed Nov 15 16:24:52 GMT 2017
Hello everybody,
together with my colleagues we are actually running some tests on a new
DSS G220 system and we see some unexpected behaviour.
What we actually see is that write performances (we did not test read
yet) decreases with the decrease of filesystem size.
I will not go into the details of the tests, but here are some numbers:
- with a filesystem using the full 1.2 PB space we get 14 GB/s as the
sum of the disk activity on the two IO servers;
- with a filesystem using half of the space we get 10 GB/s;
- with a filesystem using 1/4 of the space we get 5 GB/s.
We also saw that performances are not affected by the vdisks layout, ie.
taking the full space with one big vdisk or 2 half-size vdisks per RG
gives the same performances.
To our understanding the IO should be spread evenly across all the
pdisks in the declustered array, and looking at iostat all disks seem to
be accessed. But so there must be some other element that affects
performances.
Am I missing something? Is this an expected behaviour and someone has an
explanation for this?
Thank you,
Ivano
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