Real SMB IT: Drive Mirrors Are NOT a Backup
August 3, 2009
I was talking with the owner of an IT Services organization. His business is outsourced network and IT support, as other IT services to smaller businesses.
He told me that he was talking to a prospective client and asked what backup strategies were in place, the prospective client said he did not need any back up as the server disks were mirrored.
If you are not familiar with a basic Disk Mirror, mirroring is simply keeping two identical copies of all data on separate hard drives on the server. In the event that one disk fails, data on the other is still available until the failed disk is replaced.
Let Me Count The Ways…
1) Mirrored drives are exact replicas (exact copies) of all data written to the server drives. Well, If you accidentally delete that critical financial plan, it is deleted. Period. There is no second copy on that mirrored disk, it gets deleted too. (I have had three of those in the last two weeks. More on those in a later post)
2) Mirrored drives are designed to protect your data in the event that one disk in the mirror pair fails. That does not help you if there is a more catastrophic failure on the server. That could include the mirror controller failing among other events.
The SMB Takeaway
Single server disk mirroring can mitigate one single disk drive failure. They are not an adequate backup and recovery strategy.
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