Somebody had suggested this list for this question: I understand that dmraid is just some kind of interface to the _software_ raid that is provided on a number of SATA interface cards such as the Promise and Adaptec cards. Reading http://ata.wiki.kernel.org/index.php/SATA_RAID_FAQ I get the message loud and clear that this is not real hardware RAID but rather it's done in the BIOS on the card. The message there seems to be, if you are going to do it in software anyway, why not just skip the IO card RAID and just use MD? The one reason I could think of for using the BIOS provided RAID would be to reduce the data needing to traverse the PCI bus. With host-raid (i.e. MD) every write to disk needs to actually be written over the PCI bus twice, once for each disk, right? But do the BIOS RAID cards out there only need the write command and data once and they do the work of writing it to the two disks on-board the IO card? IIUC, when you have a BIOS RAID configured, even though there are two disks, the operating system only sees one. This would seem to support the theory that the write only goes to the controller once and it takes care of the mirroring, but I will defer to your experience. Thanx, b.
Attachment:
signature.asc
Description: This is a digitally signed message part
