raid - Is it normal for a SAS drive to have a few bad blocks, or should I replace my drive ASAP?

I have a drive—part of a RAID 1 mirror—that has two bad blocks. Adaptec Storage Manger e-mailed me when it detected the blocks. It shows 4 medium errors for that drive, but state is still “optimal”.

This is my first time using Adaptec RAID controllers. I don’t know if an occasional bad block is normal, or if I should immediately replace that drive.

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Update: The drive failed later the same day!

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The disk subsystem is:

• Adaptec 6405 with ZMM


• (2) Seagate near-line SAS drives (ST31000424SS)

The other drive hasn’t reported any bad blocks yet. I am running a consistency check.

Answer

I don’t usually answer my own question, but in this case I have a definitive answer: replace the drive ASAP. The drive in question failed later the same day.

In the early AM hours I had received three e-mails that looked like the following. That’s how I knew the drive had bad blocks, and was the only warning:

======================================================================================

ADAPTEC's EMAIL NOTIFICATION MANAGER (Instant)

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Event Type   : Warning
Event Source    : storage@HV2.domain.local
Date     : 06/29/2011
Time     : 05:29:03 AM PDT

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Event(s) List With Description
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Bad Block discovered: controller 1 (21a6e00).
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**[Note]:   This message was generated by the Adaptec Storage Manager Agent.
Please do not reply to this message.

By the end of the day, it had failed.