Jeffrey Williams-493691 (2/28/2011)

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There is a very small possibility that you could be in the middle of a transaction log backup - and the drive becomes unavailable just at the right time to cause that backup file to be corrupted.

This would cause the backup to appear to be successful - but, your log chain would still be broken.

Grant's advise on suspending the transaction log backups during this time is the best way to avoid that kind of issue - or any issues with the log chain.

If the drive is not available when the log backup starts, it will fail but it will not cause a break in the log chain. The real concern here is that you are not in the process of performing a log backup when the drive become unavailable - which could cause a break in the log chain and/or a corrupted backup file (which also breaks your log chain).