Topic: Identifying drive in RAID pair

[barryc]

I have two identical SATA hard drives, sda and sdb in a raid pair using the built-in software raid.  Hard drive sdb has just failed and been kicked out of the array.  I have got a new, identical drive to replace it, but my problem is that I cannot see any obvious way to identify the faulty drive - their part numbers etc. are the same, so the boot messages are no help.

Although the serve is backed up daily, I want to avoid risk any data loss, so I don;t want to start pulling out cables.

Is it SAFE to assume that the drive designators are assined is SATA port (as identified on the motherboard) order?

My server is V8 with latest patches on a Dell PowerEdge T110 II.

Many thanks in advance.

[Frank VB]

You can easily find out the (unique) serial number of your hard drive sda by executing this command:

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smartctl -i /dev/sda

The output will look something like this (look at the line beginning with "Serial Number":

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smartctl 5.42 2011-10-20 r3458 [i686-linux-2.6.18-348.12.1.el5] (local build)
Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital RE4 Serial ATA
Device Model:     WDC WD5003ABYX-01WERA1
Serial Number:    WD-WMAYP4866515
LU WWN Device Id: 5 0014ee 0037181ac
Firmware Version: 01.01S02
User Capacity:    500,107,862,016 bytes [500 GB]
Sector Size:      512 bytes logical/physical
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   8
ATA Standard is:  Exact ATA specification draft version not indicated
Local Time is:    Wed Aug  7 20:24:12 2013 CEST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

The serial number in question is also printed on the disk itself.

Obviously, the command

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smartctl -i /dev/sdb
will display the serial number of the second drive.

BTW, the command

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smartctl -a /dev/sda
will display all parameters of disk sda, which gives you a good idea about the "health" status of this hard drive.

[janet]

barryc

Checking the drive serial number is the best approach, as advised.

Is it SAFE to assume that the drive designators are assined is SATA port (as identified on the motherboard) order?

That is typically correct ie
port0 = sda
port1 = sdb
port2 = sdc
port3 = sdd
etc

If the drives are not plugged in sequentially to the ports then you may see something like

port0 = sda
port1 = not used
port2 = sdb
port3 = not used
port4 = sdc

[barryc]

Many thanks to both of you!

I was able to identify the drive by the serial number (they were only one digit apart!).  I checked and Janet was right sda was on the drive0 cable and sdb on drive1.

Raid now rebuilding - I wonder if the other drive is going to fail soon...

[janet]

barryc

I wonder if the other drive is going to fail soon...

That is a typical scenario, unfortunately, although not necessarily.
You would be wise to do a full disk scan on that other drive using the drive manufacturers diagnostic tools.
Otherwise (as well as) run a long test using smartctl, see
http://wiki.contribs.org/Monitor_Disk_Health

[johnp]

This is usually when I buy the bigger replacement pair and grow. YMMD