begin quoting Bob La Quey as of Sun, Dec 16, 2007 at 05:30:15AM -0800: [snip] > Yes but ... > > It seems from what I read that ZFS accomplishes all of what > hardware RAID does but without the hardware. So where lies > the hardware RAID advantage? > > I still do _not_ get it.
The advantage of hardware RAID is, as I understand it, performance. A hardware RAID controller can write to each disk in parallel, computing the necessary checksums, etc., while a JBOD with a single controller will need to write to each disk separately (if the data is to span multiple disks). Consider mirroring with software RAID (or JBOD): CPU DISK A DISK B | | | |------------->| | Hey, disk A, write <data> to <location> |<-------------| | Okay. |--------------+------------->| Hey, disk B, write <data> to <location> |<-------------+--------------| Okay | | | | | | And with hardware RAID: CPU RAID DISK A DISK B | | | | |------------>|------------->+------------>| Hey, RAID, write <data>... |<------------|<-------------+-------------| Okay | | | | That's not saying that hardware RAID controllers all *do* that; I would not be at all suprised to find out that some don't. But they *can* (and arguably *should*). -- ASCII Art is often good enough, even if not always good. Stewart Stremler -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
