On Tue, 2004-10-26 at 23:28 -0400, Lennart Sorensen wrote: > On Sun, Oct 24, 2004 at 08:28:35PM -0500, Ron Johnson wrote: > > Isn't *all* real h/w RAID "just secret proprietary software" on > > the RAID controller? Whether it be in flash or an EEPROM, real > > h/w RAID controllers have a dedicated (usually specialized) CPU > > for handling the RAID calculations, SCSI commands, RAM cache, etc. > > > > Thats why when you call up IBM, HP or Sun with a disk-related issue, > > they ask you if your SCSI cards & RAID controllers are at the latest > > ROM version. > > Well software raid is defined as raid that does the calculations in > software (on your cpu), while hardware raid does the calculations using > custom circuitry or a dedicated cpu running some software (firmware). > > If I have to waste cpu time on raid, I at least want to be able to see > the code running on my cpu and perhaps be able to improve on it. That > is the difference. Ummm, but with true h/w RAID, you are *not* wasting main CPU time on it. On "enterprise systems", the SCSI card itself doesn't even know that it's talking to a RAID set, since the SCSI cards connect to a "RAID controller", which the SCSI disks also plug into. A good example of this is/was the DEC/Compaq HSZ controllers. These are 1-Up rack-mounted computers dedicated only to managing SCSI disks in RAID configurations. 512MB battery-backed RAM, the ability to join with another controller in a dual-redundant mode (so that you had an effective 1GB of cache). I don't know how things worked in Digital Unix, but under VMS, you connect to it via SET HOST/HSZ to configure it. You could also plug a VT-220 terminal directly into it. Very convenient for initial configur- ation. Oh, and it worked with shared-disk VMS clustering. -- ----------------------------------------------------------------- Ron Johnson, Jr. Jefferson, LA USA PGP Key ID 8834C06B "Never for the sake of peace and quiet deny your convictions." Dag Hammarskjold
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