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.

Hoo Boy!

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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One Response to “Real SMB IT: Drive Mirrors Are NOT a Backup”

  1. Vicki Brown Says:

    Absolutely agree. Unfortunately many small and medium-sized business owners also believe their data is safe and secure because it’s backed up to tape. But tape as a backup method is unreliable — one or more tapes can go bad, and the data on them is often unrecoverable. Businesses should test their tape restore process and ensure it actually works at least once per year. A better alternative to tape is offsite data backup.

    Offsite data backup is one of several strategies that organizations can use to be sure that they are able to continue working both during and after any unexpected downtime or crisis. There’s an article about this in Information Systems Security:

    Full disclosure: the article is written by mindSHIFT Technologies’ Chairman and CEO, and I work for mindSHIFT.

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