James Harper <james.harper@bendigoit.com.au> writes:
If anyone has a few seconds spare, could you please run the following and post the results:
dd if=/dev/zero of=test.bin bs=512 count=128 oflag=sync
Since no one has suggested it yet, you might try bonnie++ instead.
My strace of mysql showed the behaviour: write(512 bytes) fsync() write(1024 bytes) fsync() and so on and using dd to write 512 byte chunks with O_SYNC is a good approximation of this and very consistent with the behaviour I was seeing from mysql. Initially I was looking for general performance problems but in the end it is this very specific case, and I have now proven it's not specific to this server. The reason why mysql suddenly started doing these these very small sync writes is still a mystery though. Other backup servers don't show this behaviour. James