External redundancy loss of disk

[satish]

Dear erman,



External redundancy

Oracle ASM does not provide mirroring redundancy and relies on the storage system to provide RAID functionality. Any write error causes a forced dismount of the disk group. All disks must be located to successfully mount the disk group.

We are using raid 5,do we need to take any manual action if any of the disk in external diskgroup is lost?

How does it behave for raid 10?
We are having voring disk also inexternal redundancy with raid.

Pls advise

Thanks,
Satish

[ErmanArslansOracleBlog]

Raid 5 does striping and parity.
Raid 10 does mirroring and striping.

Raid 5 gives you 1 disk fault tolerancy.
Raid 10(1+0) may give you more disk fault tolerancy. (for instance in a 4 disk RAID10 conf, if you don't lose 2 disks in the same Raid 1 at the same time...)
Bytheway, Raid 10 requires minimum 4 disks.
Raid 5 requires minimum 3 disks.

[satish]

Dear erman,

Do  we need to take any manual action if any of the disk in external diskgroup with raid protection is lost in either raid 5 or raid 10?

Thanks,
Satish

[ErmanArslansOracleBlog]

You will not fail, but you got to replace the failing disk to be in the same healthy raid configuration. When you lose a disk you may have performance problem and you will have lowered fault tolerancy. That's why you have to replace the failing disk immediately.. Rest of it will be done by the raid controller and the software of it...

[satish]

Dear erman,

Once the disk is replaced by storage admin,do we have to take any action in asm?

Thanks,
Satish

[ErmanArslansOracleBlog]

No. External redundancy is external to us.
Actually, you don't change anything from the OS perspective.. The OS disk (a lun mounted from a volume that relies on a Raid Disk Group) that ASM uses doesn't change, so you don't need to do anything extra.. In the External configuration, when a disk fails, your storage admin replaces it and then the subsequent actions are taken in the Raid controller, and it just mades the RAID whole again.. So from your perspective nothing changes.. Only you may feel some performance problem during this replacement process.