Moving Arrays

The question of changing the disks in a RAID array often arrives on Tech Support’s desk … and up until recently it’s been a an ugly one to say the least.

The basic scenario is that of a perfectly good working system running on small drives. You might have a RAID 5 array made up of 4 200gb sata drives … everything is working fine except for the fact that 600gb is not enough space any more.

Your options are pretty varied here, ranging from adding new drives to the system and expanding the array, or rebuilding the system completely on new drives, or adding drives in an external chassis connected to the server via a SAS card … OR … (and this one is not recommended), removing a drive to degrade the array, replacing it with a larger drive, rebuilding the array, then repeating the process 3 times to change all drives. This is somewhat akin to crashing your car 4 times to get 4 small dents fixed in the fender … crazy.

The sensible alternative is … move the array to a larger set of drives. To enable this you will need to be able to access all drives off the same RAID card at the same time. This could be done by putting more drives in vacant spaces in the backplane, or by directly connecting drives to the same controller via internal cabling … however you do it both the old and new drives need to be connected to the same card.

Once you can see all drives you can simply modify the array (expanding as you go if you wish), then choose the 4 new drives as the destination rather than the original 4 drives. The RAID card will then move the array from the original 4 drives to the new 4 drives … simple. Yes, it will take some time, but the result is a painless transition to newer, larger hard drives.

As for operating system volume expansion … most OS can increase the size of their volumes to make use of additional drive space (except the system volume), so this should not present many problems. You also need to make sure your operating sytem can talk to the size of the new array … remember XP still has 2TB limits on volumes, but Vista and Windows 2003/2008 are fine to talk to massive drives.

There’s one last trick in this scenario. If you are using an Adaptec 2, 3 or 5 series RAID card (SAS/SATA/Unified Serial) you can install a high port count controller beside your existing 4 or 8 port controller, reboot the system allowing the drivers to load, then shut the system down, physically move the drives to the new larger port count card and reboot … the new card will find the array on the drives, prompt you to import it then reboot perfectly.

Certainly makes life simpler.