> I don't really mean to be a hardass here, but you need to know about
> how the qmail queue works. You have the qmail source right? Included
> with that source is an "INTERNALS" document which describes how the
> queue works. With qmail's insistance on fsync'ing, you can see how
> a writeback cache on the HW RAID controller can help.
>
> Or perhaps you don't know? HW RAID controllers can come with non-volitile
> RAM caches. When part of this cache is in "writeback" mode, scsi write
> commands are put in the cache, and the controller tells the OS that the
> command has been completed. Then the writes are committed to hard drive
> (which have their own caches). Thus, multiple small-block writes followed
> by fsync's should finish much quicker on a HW RAID with writeback cache.
>
> If you're relying on OS RAM to do the same thing for a filesystem, then
> the fsync will put an end to that.
All this would make hw-cach *forbidden* for qmail queue dir, since then it
is *not* guaranteed, that what is synced is writted on disk and will
survive a power loss....
Anyway, what is noone mentioning raid 5? I just played with it under linux
(software raid) until now - but it seems quite fast.
Greetings, Florian Pflug
