dmx spare disk in disk group

correct, if you run

symdisk list -sid -by_diskgroup -hotspares

you will see all the hotspares in the box. On my DMX3/DMX4 and VMAX ..all hot spares reside in the same disk group 0

is this true for both DMX and VMAX? Hot spare is not limited to work within a diskgroup only.

These are global hotspares

in that case. I guess my question is still open. the dmx has 2 diskgroup

diskgroup 0 has total 484 disk where 12 are spare disk.

and diskgroup 1 has 476 disk and there is no spare disk.

There is no hot spare diskgroup in my dmx. symdisk -sid yyyy list -hotspare -by_diskgroup shows hot spare disk of diskgroup 0 only.

so will the diskgroup 1 be able to take hot spare disk from diskgroup 0 when required?

i don't have any systems running on 75 yet, maybe things changed in 75 or maybe that's just how your CE build the bin file.

DMX-3 supports both dynamic and permanent sparing, but the disk groups don't really matter for either.

For dynamic sparing, all spares can cover all data drives.

For permanent sparing, only spares of exact same drive "type" can be used.  Think of it as a drive replacement.  If we were going to physically replace a drive, we would need to use a drive that is same size, speed, technology, etc.  The DMX-3 spares of each type of drive will be placed in their own disk group and can be used to replace like data drives.

The disk groups in 5875 are a bit different.  Spares are in not in their own group anymore.  Instead they are in included in the data drive groups. However the permanent sparing behavior is the same.  A spare can be used by other disk groups of same drive types.

In 5874 code all of our hot spares were listed as being in disk group 0.  In 5875 code it appears that disk group 0 is no longer presented and when you look at disk groups in SMC (for instance) you will see a # of spares tab.  Now if you have multiple groups of the same drive type they may not all show # of spares as any spare that meets the appropriate requirements will be used.

yes, all above are correct.

the summary:

1. before 5874 code, disk groups start from 0 by default, but most EMC CD/IDE are asked to NO use disk group 0 except spare disk group. That's why you may still see disk group 0 but it's spare disk group.
   
2. From 5875 code, spare disks are grouped into data disk groups (low case "type" and yellow color  in symmwin "disk" window, but data disks are in up case). Though there may be many spare groups, but they work globally.