On Tue, Nov 23, 1999 at 02:04:50AM +0000, Florian G. Pflug wrote:
> > 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....
Not true. It's important to have a NVRAM cache; NV as in non-volitile
to survive a power outage.
> Anyway, what is noone mentioning raid 5? I just played with it under linux
> (software raid) until now - but it seems quite fast.
RAID 5 write performance is either as bad or worse than RAID 1.
John
