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Archive for May 7th, 2011

SCSI Hot Swap Hard Disks

Saturday, May 7th, 2011

When using and operating a high availability server or system within an organisation, you need to consider that there may be times when hardware fails and the system may be offline. This is par for the course when it comes to computers. No system in 100% fail safe as there are so many things that can go wrong. One of the main issues that IT departments face is loss of data if a disk fails. A way to overcome this issue is to employ a level of RAID and use SCSI hot swap disks.

Using RAID allows you to spread your data across many disk drives in the server. This process has several levels of complexity and redundancy and allows you to recover information from a failed disk using parity information, written to different disks. A little like an algebra sum, where 1 + a = 3 (a = 2), RAID allows the data to be recreated when the faulty hard disk is replaced. The server still operates, but it has to work out the sums on its own, making it slightly slower.

In the past, it was a requirement that the server hardware was powered off to replace the hard disk, but hot swap drives and caddies have allowed the server to continue to operate whilst the data is recovered. SCSI hot swap drives allow you to remove the faulty hard disk and insert a new one without having to power off any part of the server. This allows the server to continue running whilst the new disks is restored or repaired and made part of the RAID array. Each major manufacturer of server hardware has a slightly different implementation of the hot swap technology. The SCSI hard disk sits in a caddy or tray which is specific to each server brand. The SCSI disk itself is sometimes independent to the server brand, and therefore any similar size SCSI disk can be used..