Convert Raid 5 to Raid 1

[Anjum Shafique]

I have HP proliant ML370 wiht SA642 controller having 3x300 GB ultra SCSI on RAID 5 and 3x72.8 GB ultra SCSI also with RAID 5 using internal channel. I want to convert 3x72.8 GB SCSI's to RIAD 1 without loosing the data. How I do???

[TTr]

This is called RAID migration. The problem in your case is that you have 3 drives in your 73GB raid group and with raid1 you need to have an even number of drives. So you need to add a 4th drive in the array group and then do the drive migration.
It looks like you have an older ML370 to support UltraSCSI drives so if you have an available drive slot in the drive cage, you can add a 4th drive. Otherwise you have to save your data, destroy the 3 disk raid5 group, create a new raid1 group and reload your data. If your 3-disk raid5 group has more than 50% allocated in LUNs you would definitely need a 4th drive, it it uses less than 50% space, you can get away with a 2-drive raid1 group.

[Anjum Shafique]

Thanks for your reply, we have a SA642 controller that have the option have battery backed cache enabler, so if we install this what happened when we migrate to raid withour adding the 4th hdd, rather there is no space for 7th hdd.

[TTr]

There are several problems with what you are trying to do.
1. Removing drives from an existing raid group is a feature that the SA642 must support. Larger arrays do support it but it is not mentioned in the 642 features.
2. Enough free space must exist in the 3x73GB raid5 group, the equivalent of a single disk.
3. A 3-disk raid5 drive makes sense but a 2-disk raid5 does not. So even if the 642 has the disk reduce feature it might not let you reduce this particular disk.
4. Similar to step2 the remaining space in the raid group must be less than 73GB to be able to fit in a 2-disk raid1 group otherwise it is not possible to do it.

Note that disk reduction and raid migration are two different operations. You can try raid migration to see what happens.

Item 4 must be true even if you decide to backup the data, destroy the raid5 group, create a raid1 group and restore the data.