On 22/08/12 22:24, David McBride wrote:
On 22/08/12 09:54, Denis Fondras wrote:
* Test with "dd" from the client using CephFS :
# dd if=/dev/zero of=testdd bs=4k count=4M
17179869184 bytes (17 GB) written, 338,29 s, 50,8 MB/s
Again, the synchronous nature of 'dd' is probably severely affecting
apparent performance. I'd suggest looking at some other tools, like
fio, bonnie++, or iozone, which might generate more representative load.
(Or, if you have a specific use-case in mind, something that generates
an IO pattern like what you'll be using in production would be ideal!)
Appending conv=fsync to the dd will make the comparison fair enough.
Looking at the ceph code, it does
sync_file_range(fd, offset, blocksz, SYNC_FILE_RANGE_WRITE);
which is very fast - way faster than fdatasync() and friends (I have
tested this ... see prev posting on random write performance with file
writetest.c attached).
I am not convinced the these sort of tests are in any way 'unfair' - for
instance I would like to use rbd for postgres or mysql data volumes...
and many database actions involve a stream of block writes similar
enough to doing dd (e.g bulk row loads, appends to transaction log
journals).
Cheers
Mark
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