Gehr, Chuck R writes:
> One word of caution about random writes. From my experience, they are
> not nearly as fast as sequential writes (like 10 to 20 times slower)
> unless they are carefully aligned on the same boundary as the file
> system record size. Otherwise, there is a heavy read penalty that you
> can easily observe by doing a zpool iostat. So, depending on the
> workload, it's really a stretch to say random writes can be done at
> sequential speed.
>
> Chuck
>
Could we agree on saying that
partial writes to blocks that are not in cache are much
slower than writes to blocks that are.
Then given that Sequential pattern can benefit from
readahead, then those will fall in the fast category most of
the time. Performance of Random writes will depend on the
cached ratio. For DB working sets that greatly exceeds
system memory, which is common, then this fall in the slower
case and this stays true for any filesystem.
Or said otherwise, There is no free lunch.
-r
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
