Clarification - Re: RAID-DP

BTW, I should have clarified in my original note that the original statement that was made was NOT as a result of any NetApp presentation/slides. It is very obvious from the numerous very helpful responses that I received from all of you is that the original statement was ABSOLUTELY not the case at all and it does work !

Thanks George

On Mon, 04 Apr 2005 12:39:15 -0400 (EDT), George Kahler george@yorku.ca wrote:

Thanks Adam and to others for clearing up the misconception. George

On Mon, 4 Apr 2005 09:17:09 -0700, "Fox, Adam" Adam.Fox@netapp.com wrote:

...

This is absolutely false. I heard this strange misconception with RAID-4 too. (If you lose the parity disk, the whole thing falls down because it's all on 1 disk).

Here's a lab box to make you feel better.

Volume test (online, raid_dp) (block checksums) Plex /test/plex0 (online, normal, active) RAID group /test/plex0/rg0 (normal)

  RAID Disk Device  HA    SHELF BAY CHAN  Used (MB/blks)    Phys

(MB/blks) --------- ------ --------------- ---- --------------

---

  dparity   0b.20   0b    1     4   FC:B  68000/139264000

69536/142410400 parity 0b.21 0b 1 5 FC:B 68000/139264000 69536/142410400 data 0b.28 0b 1 12 FC:B 68000/139264000 69536/142410400

Spare disks (empty)

(note: No spares)

filer> disk fail -i 0b.20 filer> disk fail -i 0b.21

Now, here's sysconfig -r again:

Volume test (online, raid_dp, degraded) (block checksums) Plex /test/plex0 (online, normal, active) RAID group /test/plex0/rg0 (double degraded)

  RAID Disk Device  HA    SHELF BAY CHAN  Used (MB/blks)    Phys

(MB/blks) --------- ------ --------------- ---- --------------

---

  dparity   FAILED          N/A                   68000/139264000
  parity    FAILED          N/A                   68000/139264000
  data      0b.28   0b    1     12  FC:B  68000/139264000

69536/142410400

Spare disks (empty)

Broken disks

RAID Disk Device HA SHELF BAY CHAN Used (MB/blks) Phys (MB/blks)

---

---

admin failed 0b.20 0b 1 4 FC:B 68000/139264000 69536/142410400 admin failed 0b.21 0b 1 5 FC:B 68000/139264000 69536/142410400

Still running..but degraded.

-- Adam Fox adamfox@netapp.com

-----Original Message----- From: George Kahler [mailto:george@YorkU.CA] Sent: Monday, April 04, 2005 11:22 AM To: toasters@mathworks.com Subject: RAID-DP

At a recent NetApp presentation it was mention in passing that RAID-DP fails if a double disk failure happens to hit the two parity disk.

Is this true ?

George