MessageSpares not only cross shelves they even cross FCAL adapters if you have shelves on different FCAL HBAs.
A single volume would have to lose two disks simultaneously or two disks after the first rebult in order to lose data with only one spare.
If it lost one disk, then shortly thereafter another disk, then having a second spare would not help as the first one would still be rebuilding and you'd lose the volume.
If you lose one disk, rebuild, and lose another disk, you're still intact but in degraded mode and vulnerable. Having a second spare would be helpful. But the odds of losing two disks, the second one after the first one rebuilt but before NetApp got you a replacement 4 hrs or the next day, seems low.
If you have two spares per filer like Sam mentioned, you're covered anyway since hot spares are global to the entire filer.
Gosh this sounds convoluted! :-)
MD
----- Original Message ----- From: Steve Evans To: Tom Yergeau Sent: Wednesday, August 07, 2002 4:35 PM Subject: RE: # of volumes
Well if you have a 14 disk shelf, and two volumes, then each volume could have a disk fail on top of one more that the spare would cover. But yeah, if your doing a 1:13 ratio then it doesn't matter anyways because I don't believe spares can cross shelfs.
Steve Evans Computing Services (619) 594-0653
On Wed, Aug 07, 2002 at 05:26:11PM -0400, Tom Yergeau wrote:
If you lose one disk, rebuild, and lose another disk, you're still intact but in degraded mode and vulnerable. Having a second spare would be helpful. But the odds of losing two disks, the second one after the first one rebuilt but before NetApp got you a replacement 4 hrs or the next day, seems low.
If you have multiple filers, another option is to have one hot spare per filer, plus one or two cold spares sitting in a box, so you can plug a new disk in right away. Of course, this only works if there is someone on site to plug it in. For a lights out operation, I would probably feel more comfortable with two hot spares.
Also, if you have multiple disks sizes in a filer, you will want one hot spare for each disk size.
-- Deron Johnson djohnson@amgen.com
Spares can fill in for drives smaller than the spare, so technically as long as your spare is the same size as your largest drive, you're okay. So if you have 18, 36 and 72 GB drives and a 72 GB spare, and you lose an 18 GB drive, then the 72 GB spare will take over for it.
On the downside, that disk is now a permanent member of the RAID set and you've lost all that extra space. The only way I know of to reclaim it would be to replace the failed 18 GB drive, then do a disk fail on the 72 GB drive, let it rebuild onto the 18 GB drive, then disk erase the 72 and put it back in as a spare. Big PITA.
Generally, I prefer to keep a spare for each disk size. Life is easier that way.
On Thu, 8 Aug 2002, Deron Johnson wrote:
Also, if you have multiple disks sizes in a filer, you will want one hot spare for each disk size.
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Deron Johnson -
Tom Yergeau -
Tom Yergeau