Hard Disk – Retrieve Info Behind Hardware RAID Controller

hard-diskraid

If I run smartctl -i /dev/sdb I get correct disk information including serial number and drive model number. But this is for a disk marked as JBOD.

For n drives that are RAID'ed (using an LSI RAID card in my case), that presents the assembled volume to Linux under just dev/sda for example, and I make one partition that would be sda1 and is of the expected size… fairly simple.

Without having to power off my server and remove each drive to look at the sticker for model and serial information, is there a way to see each individual disk behind a RAID card that has been combined into a virtual drive, and get the basic information of any one of those RAID'ed disks?

Best Answer

Since you mention an LSI RAID card, I’ll assume it’s a MegaRAID device; in this case, you can get the information about each underlying drive by running

smartctl -i -d megaraid,0 /dev/sda

replacing /dev/sda as appropriate (it should correspond to the device node of your RAID drive as visible in the system), and 0 (increment it to see each drive).

The smartctl manpage lists the different types of controllers which are supported, and the syntax used to address them.

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mdadm – Rebuilding IMSM RAID-0 Array from Disk Images Using mdadm

Looking at the partition table for /dev/loop0 and the disk image sizes reported for /dev/loop0 and /dev/loop1, I'm inclined to suggest that the two disks were simply bolted together and then the partition table was built for the resulting virtual disk:

Disk /dev/loop0: 298.1 GiB, 320072933376 bytes, 625142448 sectors

Device       Boot   Start        End    Sectors   Size Id Type
/dev/loop0p1 *       2048    4196351    4194304     2G  7 HPFS/NTFS/exFAT
/dev/loop0p2      4196352 1250273279 1246076928 594.2G  7 HPFS/NTFS/exFAT

and

Disk /dev/loop1: 298.1 GiB, 320072933376 bytes, 625142448 sectors

If we take the two disks at 298.1 GiB and 298.1 GiB we get 596.2 GiB total. If we then take the sizes of the two partitions 2G + 594.2G we also get 596.2 GiB. (This assumes the "G" indicates GiB.)

You have already warned that you cannot get mdadm to recognise the superblock information, so purely on the basis of the disk partition labels I would attempt to build the array like this:

mdadm --build /dev/md0 --raid-devices=2 --level=0 --chunk=128 /dev/loop0 /dev/loop1
cat /proc/mdstat

I have a chunk size of 128KiB to match the chunk size described by the metadata still present on the disks.

If that works you can then proceed to access the partition in the resulting RAID0.

ld=$(losetup --show --find --offset=$((4196352*512)) /dev/md0)
echo loop device is $ld
mkdir -p /mnt/dsk
mount -t ntfs -o ro $ld /mnt/dsk

We already have a couple of loop devices in use, so I've avoided assuming the name of the next free loop device and instead asked the losetup command to tell me the one it's used; this is put into $ld. The offset of 4196532 sectors (each of 512 bytes) corresponds to the offset into the image of the second partition. We could equally have omitted the offset from the losetup command and added it to the mount options.

Best Answer

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