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I have an external drive bay with 4 eSATA disks in it. My system has a 4-port eSATA card, as well as a pair of internal hardware RAID1 drives. The external drives are in software RAID1 pairs as /dev/md0 and /dev/md1. Both have been configured as LVM physical volumes to create my storagevg LVM volume group. Recently, a single drive went offline (I suspect cables), but there does not seem to be a good way to physically identify which drive I need to check, especially since initialization order isn't the same between boots. How can I find the disk needing attention?

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7 Answers 7

up vote 12 down vote accepted

Disk Utility (sitting in System -> Administration) will give you the serial numbers for all your disks.

Here's what I see (look at the top-right for the serial). You'll notice that this drive is within a mdadm RAID array. Disk Utility can penetrate the array for raw disk access.

Disk Utility

I have 6 of the same model of disk in my PC so I drew a little diagram showing their position in the case and the serial number so I can locate them quickly on serial in an emergency.

The opposite is also true in that if a disk dies, I just need to find which disks are showing up and I can eliminate them until I know which serial is missing.

Edit: I'm trying to improve my bash-fu so I wrote this command line version to just give you a list of disk serial numbers that are current in your machine. fdisk may chuck out some errors but that doesn't taint the list:

for disk in `sudo fdisk -l | grep -Eo '(/dev/[sh]d[a-z]):' | sed -E 's/://'`;
do
    sudo hdparm -i $disk | grep -Eo 'SerialNo=.*' | sed -E 's/SerialNo=//';
done

(And you can crumble that into one line if you need to - I've broken it up for readability)

Edit 2: ls /dev/disk/by-id/ is somewhat easier ;)

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Using serial numbers can work nicely if one has already recorded them externally. In the case of a system that can't be powered off but has hot-swap drives, it'd be nice to be able to locate the failed drive via LEDs. –  Kees Cook Nov 3 '10 at 16:51
    
You'll also notice that there's a "Location" identifier in Disk Utility, showing which port of the host adaptor the drive is plugged in. You might be able to divine which ports are which without unplugging the drives but I can't speculate to this actually working. –  Oli Nov 3 '10 at 17:11
    
In your case, stopping the raid array down for 5 minutes, unplugging each drive and getting the serial shouldn't be too unreasonable and shouldn't require turning the machine off... But the RAID would have to be taken down unless you fancy it rebuilding. –  Oli Nov 3 '10 at 17:13
    
"Location" is not always useful, e.g. in case of PATA there are often 2 disks on 1 port, and if your disks are both set to "AUTO" for master/slave negotiation, there is probably no way to find out which is which? It might work for SATA though –  JanC Nov 3 '10 at 18:19
1  
Do PATA drives still exist? I've been SATA-only since... Well since a 112gig disk was considered big. The finding-the-port problem doesn't really count here because we're talking about an external drive bay. But sure. On consumer motherboards, you'll probably need to consult the manual to get an idea what port is what... Even then, software might attribute them a different order. –  Oli Nov 3 '10 at 18:22

It's simple. This for example is the output on my PC:

andrea@centurion:~$ cat /proc/mdstat 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdh1[1] sdg1[0]
      312568576 blocks [2/2] [UU]

unused devices: <none>

as you can see I've /dev/sdh1 and /dev/sdg1 joined in /dev/md0

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Right, but this doesn't tell me anything about where they are physically in the external drive enclosure. –  Kees Cook Nov 3 '10 at 1:33

With software raid this is a common issue. Hardware raids tend to have a feature that allows you to blink the LED associated with a drive, assuming that your hardware supports that.

But with software RAID each drive has some unique metadata. Which you can read it from each drive using the command mdadm -E /dev/sda1 for each drive in the the array, modifying the devices to match your environment. So if you have a situation where a drive is giving you problems and is currently offline. I would run this on each drive that is online, recording the minor number for each drive. Then using a Live CD that supports MD, system rescue cd is a good one, with only one drive at a time connected and running this command to find the culprit. This probably isn't as straight forward as you'd like but it should work.

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Perhaps there might be serial numbers you can get through Linux that are also printed on the physical drive? –  erjiang Nov 3 '10 at 2:02

The info that udisks gives (either on the commandline or in the GNOME Disk Utility) includes the disk serial number. On the disks I have, the serial number is printed on the upper side and on the front side (the one on the other side of the one that contains the connectors), both as numbers and with a barcode. Unfortunately, most PC cases make it impossible to read those serials without pulling the disk out...

You can also find the serial numbers in /dev/disk/by-id/.

As your disk is off-line, I assume it isn't "seen" by the kernel currently? In that case, you might have to go by elimination: you want the disk with a serial number that is not listed...

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If you have trouble matching the drive serial number or port indication with your disks' spatial locations, you can run cat /dev/sdz >/dev/null (where sdz is the failed drive) and locate the drive by its LED (or by ear if you aren't in a noisy server room). If the drive won't even power up, that should be enough to tell which one it is. Be sure to put a visible label on the disks for next time.

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lsscsi

$ lsscsi -l
[0:0:0:0]    disk    ATA      TOSHIBA THNS128G AGLA  /dev/sda
  state=running queue_depth=1 scsi_level=6 type=0 device_blocked=0 timeout=30
[1:0:0:0]    cd/dvd  HL-DT-ST DVDRAM GT30N     LT09  /dev/sr0
  state=running queue_depth=1 scsi_level=6 type=5 device_blocked=0 timeout=30

if the disk is not in state running, that's a pretty good sign. So /proc/mdstat will tell you which member failed. Assuming you don't have a nice drive cage you'll have to drill down by serial number, sg_inq should help with that.

If you do have a good drive cage, you should be able to enable the disk beacon to help identify the faulty member.

http://www.mail-archive.com/linux-scsi@vger.kernel.org/msg07307.html

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Kees,

Since your array doesn't have SES smarts and the disk activity LED isn't directly drivable e.g. you need firmware support for that. The only other thing you can do is quiesce the IO as best you can and then use something like dd or sg_read on the members themselves to stride a pattern of reads to the disk that creates a uniquely identifiable blink pattern using the activity LED, a poor mans beacon if you will. It's really your only alternative, unless bringing the array down is an option.

This kind of serviceability is what differentiates external storage arrays. Since you didn't plan ahead by scribbling down the serial numbers and their positions, you can't do the simple set difference to identify the faulty drive. It's the price you pay for the solution you deployed, whether you realize it or not, but hey, live and learn.

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