Quoting <15AD5D7936F8D21198240000F831776E3E81AB at dboexc1.dbo.cpqcorp.net>
by "Jakma, Paul" <Paul.Jakma at compaq.com>:
> > Even with writeback, any raid5 implementation I've used (*) has
> > sucked. You
> then the controller is parity-bound. RAID5 should be faster at
> writing than RAID1 if the controller can do the parity calculations
> fast enough.
How's that, then? The minimum sensible RAID5 is three disks, so every
write involves writing to at least three disks, plus the parity
calculation time. By contrast, a mirror requires 2 disks and two
writes. If the mirrors are located on seperate controllers for
controller redundancy, the SCSI layer can even dispatch the writes
concurrently to the two controllers.
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