>>     Even for RAID5 ? it uses a bit more CPU for the parity calculations.

> I honestly can't speak to RAID 5. I don't (and won't) use it. RAID 5 is 
> a little brutal when under
> heavy write load. I use either 1, or 10.

Yes, for RAID5 software RAID is better than HW RAID today - the modern general 
purpose CPUs are *much* faster at the ECC calculations than the CPUs on most 
modern hardware SCSI RAID cards.

Note that there is a trend toward SATA RAID, and the newer crop of SATA RAID 
adapters from companies like 3Ware are starting to be much faster than software 
RAID with lower CPU consumption.

Use non-RAID SCSI controllers if you want high performance and low CPU 
consumption with software RAID.  The write-combining and TCQ of SCSI is well 
suited to SW RAID.  Note that if you use HW RAID controllers for SW RAID, 
expect slightly better performance than in their HW RAID mode, but much higher 
CPU consumption, as they make for terrible JBOD SCSI controllers.  This is 
especially true of the HP smartarray controllers with their Linux drivers.

- Luke

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