From: Jeff Kennedy (
Date: Thu Feb 18 1999 - 16:13:38 CST

Thanks to the great many of you who have confirmed my belief about how
RAID5 is SUPPOSED to work. At the moment I have a call in to SUN software
support about this and am waiting to hear back. I have several RAID1
volumes in this same array and when I lost a disk in one of these Veritas
dropped the failed disk, pulled in the hot spare, and recreated the mirror.
All with no intervention from me. That's how RAID5 should work as well.

If anyone is interested in how this is finally resolved please let me know
and I will mail you. If there are enough requests I will post an
additional summary.

Again, thanks to everyone.

Jeff Kennedy

Hello All,

I have a serious quandry. I have an E3500 with an A5000 attached running
Solaris 2.6 with Veritas Volume Manager (don't know what version). One
volume (u05) is a 12 disk RAID5 configuration that houses an Oralce
database. Over the weekend we lost a disk on this volume and Veritas
dropped the whole volume. When the SUN engineer came out to replace the
disk she said that that was normal, if you lose a disk under software RAID5
the whole filesystem will be inaccessible until you replace the disk, at
which time the filesystem will rebuild the data on the new disk and sync up
(this is another issue, why would the ENTIRE fs need to sync to rebuild the
data from parity?).

My problem: as I understand RAID5, when you lose a disk all writes are
done to the remaining disks and any read of data from the failed disk is
recreated on the fly from parity. When RAID5 is running in degraded mode
like this the system takes a huge hit in resources, only natural given the
cpu cycles required. But SUN is trying to tell me that that's not the
case. What's the point of RAID5 then? I know for a fact that NT will do
exactly what I'm explaining because I've done it myself; like I said, the
system slows to a crawl but it's still crawling, not dead. So SUN is
saying that an OS that isn't mature enough yet for the Enterprise has
better RAID5 capability? What a crock.

Can anyone confirm my understanding of RAID5? Or explain why SUN doesn't
work as well as NT in this area?


Jeff Kennedy

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