I should mention one other "annoying" behavior - when a disk drops from the filer, is not marked as "failed" and no autosupport is issued.  So, you can have a missing disk that the filer will spare out, using whatever spare(s) you have provided.  However, unless you monitor for this condition by comparing disks total counts to what should be there, its possible to have a failure, use your spare, not replace the spare and get a second failure.  This condition does exist under 6.1R1 - it may be fixed in later ONTap revs.  In this scenario, having 2 or more spares is very good indeed.
-----Original Message-----
From: Tom Yergeau [mailto:yergeau@yergeau.net]
Sent: Wednesday, August 07, 2002 2:26 PM
To: Steve Evans; toasters@mathworks.com
Subject: Re: # of volumes

Spares 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