Unfortunately, a storage-based RAID controller cannot detect errors which occurred
between the filesystem layer and the RAID controller, in either direction - in or
out. ZFS will detect them through its use of checksums.
But ZFS can only fix them if it can access redundant bits. It can't tell a
storage device to provide the redundant bits, so it must use its own data
protection system (RAIDZ or RAID1) in order to correct errors it detects.
Gregory Shaw wrote:
Most controllers support a background-scrub that will read a volume and
repair any bad stripes. This addresses the bad block issue in most cases.
It still doesn't help when a double-failure occurs. Luckily, that's
very rare. Usually, in that case, you need to evacuate the volume and
try to restore what was damaged.
On Jun 26, 2006, at 6:40 PM, Eric Schrock wrote:
On Mon, Jun 26, 2006 at 05:26:24PM -0600, Gregory Shaw wrote:
You're using hardware raid. The hardware raid controller will rebuild
the volume in the event of a single drive failure. You'd need to keep
on top of it, but that's a given in the case of either hardware or
software raid.
True for total drive failure, but not there are a more failure modes
than that. With hardware RAID, there is no way for the RAID controller
to know which block was bad, and therefore cannot repair the block.
With RAID-Z, we have the integrated checksum and can do combinatorial
analysis to know not only which drive was bad, but what the data
_should_ be, and can repair it to prevent more corruption in the future.
- Eric
--
Eric Schrock, Solaris Kernel Development http://blogs.sun.com/
eschrock
-----
Gregory Shaw, IT Architect
Phone: (303) 673-8273 Fax: (303) 673-8273
ITCTO Group, Sun Microsystems Inc.
1 StorageTek Drive MS 4382 [EMAIL PROTECTED] (work)
Louisville, CO 80028-4382 [EMAIL PROTECTED] (home)
"When Microsoft writes an application for Linux, I've Won." - Linus
Torvalds
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
--
--------------------------------------------------------------------------
Jeff VICTOR Sun Microsystems jeff.victor @ sun.com
OS Ambassador Sr. Technical Specialist
Solaris 10 Zones FAQ: http://www.opensolaris.org/os/community/zones/faq
--------------------------------------------------------------------------
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
