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+Title: How to figure out which RAID disk to replace when it fail
+Tags: english, raid
+Date: 2012-02-14 21:25
+
+<p>Once in a while my home server have disk problems.  Thanks to Linux
+Software RAID, I have not lost data yet (but
+<a href="http://comments.gmane.org/gmane.linux.raid/34532">I was
+close</a> this summer :).  But once a disk is starting to behave
+funny, a practical problem present itself.  How to get from the Linux
+device name (like /dev/sdd) to something that can be used to identify
+the disk when the computer is turned off?  In my case I have SATA
+disks with a unique ID printed on the label.  All I need is a way to
+figure out how to query the disk to get the ID out.</p>
+
+<p>After fumbling a bit, I
+<a href="http://www.cyberciti.biz/faq/linux-getting-scsi-ide-harddisk-information/">found
+that hdparm -I</a> will report the disk serial number, which is
+printed on the disk label.  The following (almost) one-liner can be
+used to look up the ID of all the failed disks:</p>
+
+<blockquote><pre>
+for d in $(cat /proc/mdstat |grep '(F)'|tr ' ' "\n"|grep '(F)'|cut -d\[ -f1|sort -u);
+do
+    printf "Failed disk $d: "
+    hdparm -I /dev/$d |grep 'Serial Num'
+done
+</blockquote></pre>
+
+<p>Putting it here to make sure I do not have to search for it the
+next time, and in case other find it useful.</p>
+
+<p>At the moment I have two failing disk. :(</p>
+
+<blockquote><pre>
+Failed disk sdd1:       Serial Number:      WD-WCASJ1860823
+Failed disk sdd2:       Serial Number:      WD-WCASJ1860823
+Failed disk sde2:       Serial Number:      WD-WCASJ1840589
+</blockquote></pre>
+
+<p>The last time I had failing disks, I added the serial number on
+labels I printed and stuck on the short sides of each disk, to be able
+to figure out which disk to take out of the box without having to
+remove each disk to look at the physical vendor label.  The vendor
+label is at the top of the disk, which is hidden when the disks are
+mounted inside my box.</p>
+
+<p>I really wish the check_linux_raid Nagios plugin for checking Linux
+Software RAID in the
+<a href="http://packages.qa.debian.org/n/nagios-plugins.html">nagios-plugins-standard</a>
+debian package would look up this value automatically, as it would
+make the plugin a lot more useful when my disks fail.  At the moment
+it only report a failure when there are no more spares left (it really
+should warn as soon as a disk is failing), and it do not tell me which
+disk(s) is failing when the RAID is running short on disks.</p>