bad block allocation

[Ray Herbig]

Quick question can any harm come from turning bad block allocation off. Turning it off on logical volumes that are comprised of EMC physical disks, that is.

Thanks,
ray

[James R. Ferguson]

Hi Ray:

EMC advises users to do this. However, see document #1100331419 (LVM: Bad Block Relocation policy on EMC with mirrored logical volumes) for some interesting twists.

...JRF...

[Jim Moffitt_1]

I believe you are supposed to turn off bad block allocation when using the EMC disks.

[Rita C Workman]

As James said EMC advises you do this.
Reason being, if something occurs and HP's Bad Block Re-allocation is ON, then HP will reallocate and controls where it 'put things'. Unfortunately, it does not pass that re-route on to EMC. Now that's where the problems begin....because now EMC (which has it's own reallocation policy) can't find where things went.

So if your connected to an EMC disk array...turn it off on all existing and new lvols.

/rcw

[Bill McNAMARA_1]

yes the array (xp too) does it's own hardware bb relocation.

lvcreate -r n vgxp_or_emc

Later,
Bill

[Tim Malnati]

As a general rule, you should turn off bad block realocation on an EMC array (or any array equipment that handles it internally). The document that Jim is refering to involves situations where you have HPUX Mirrordisk mirroring two or more EMC areas. This is very unusual where the EMC array is already handling redundancy internally. In cases where a shop wants to split off a volume for backups or whatever, the EMC Timefinder product is much cleaner and has many more capabilities than Mirrordisk ever will.