Bond Masuda wrote: > Also, one thing that I've notice makes a big performance difference on the > SAS/SATA controllers in Dell servers is the block device read-ahead cache I/O > scheduler. To see what your read-ahead cache looks like: > > blockdev --getra /dev/sda (or whatever the device is) > > To set it: > > blockdev --setra 8192 /dev/sda (set it to 8MB) > > I don't know about mirror sets, but with RAID-5 sets, read-ahead tuning made > a big difference in throughput tests. >
While that read-ahead value will help a linear read bench mark, what does it do for random-access? If you have a few milliseconds delay between each seek you might end up reading lots of extra sectors into the disk cache, invalidating other data that might actually be accessed again. Theoretically, that is... Dunno about actual practice, as I suppose it would depend on workload... If I'm writing to a blockdev (like copying files to a file system), it has to do some reads to pull in the directories -- will having it set to read another full 8MB after each dir read affect write performance? I don't know, but seems like it 'could'... ?? -l _______________________________________________ Linux-PowerEdge mailing list [email protected] https://lists.us.dell.com/mailman/listinfo/linux-poweredge Please read the FAQ at http://lists.us.dell.com/faq
