Managing RAID on Linux

Manual Disk Replacement

Even if online spare disks are used, system administrators must physically replace failed drives. Replacement should take place as soon as possible to avoid the potential for a secondary disk failure that might incapacitate an array. A secondary disk failure, when no more spares are available, means that the array will operate in degraded mode until the disk can be physically replaced. It’s also advisable to replace dead disks as soon as possible so they can be reallocated as spares in the event of another failure.

Remember that ATA does not technically support any hot-swap capability. Although some newer disk enclosures and controllers support this feature, disk manufacturers and reports from users discourage the use of hot-swap ATA. Therefore, set up hot-swap ATA equipment at your own risk.

Likewise, SCSI supports hot-swap only when working with SCA drives. Although some users have successfully swapped non-SCA SCSI disks out of running systems, this practice is not recommended.

If your system supports SCA disks, you can simply remove the drive and add a new one. The SCSI bus needs to be told that a new disk is present, because the Linux kernel or the hardware disk controller will have already marked the failed disk as nonoperational when it entered the reconstruction phase.

Using the /proc/scsi interface, disks can be added and removed from a running system. To remove a failed disk from the bus (if the kernel hasn’t already removed it), use the following command: ...