What do RAID1 and RAID5 really mean?

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Hi,

I have got some questions about RAID1 and RAID5 hardware solutions. For example, I implemented RAID1 as disk mirroring in Windows Server 2003. How do I test this disk mirroring in action in the real world? Does it mean if one hard drive has failed, the system will continue to operate on the mirrored drive? Or when one hard drive has failed, the system will fail but one can reboot the system to the mirrored drive?

Similarly, if I implement a RAID5 using 3 disks, what does it really do? Does it support failover, data redundancy or both? How does RAID5 achieve it?

Posted 15-May-09 7:23am

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Sebastian Schneider · Accepted Answer · 2009-05-15T12:38:00

You can test disk mirroring by trashing one of the drives. If they are hot-swapable, just yank one out and put in a new, empty disk. The system will continue to operate during all this, though possibly slower than usual during the rebuild.

RAID-5 with three disks:
Basically, it writes 1 sector to disk 1, 1 sector to disk 2, then checksum of the two sectors to disc 3. The steps are repeated, but the checksum is always written to a different disk. That way, two disks are enough to rebuild the array, it does not matter which disk failed, AND it ofers speed advantages compared to RAID-1.

RAID as such does not offer failover. All disks are in use all the time. However, some RAID-cases have hot-standby-disks, which automatically replace failed ones, in order to keep the window of vulnerability as short as possible.
There also is no real data redundancy: If you accidentally delete something, its lost.

RAIDs only increase uptime and, to a certain amount, throughput.

And now my significant other has entered the room and ordered me to stop typing.

So long.