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Roger Creasy
Asked: 2016-08-13 05:15:09 +0800 CST

How do I determine which virtual disk is which in Linux?

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I have a Linux server running on a VMware virtual machine, with 4 virtual hard drives. After the box ran for a month, I added 2 of the 4 hard drives in the vSphere client; I need more space. I did this step a few weeks ago, then was pulled into another project before creating the file systems and setting up mounts. Now, I do not know which drive is which within Linux. I have /dev/sda , /dev/sda1, /dev/sda2, and /dev/sdb

How do determine which drives have existing data and which are the new? Or, how do I remove drives and start over (I know how to remove the drives in teh vSphere client, but not how to remove the references to them in Linux).

Here are the results of dmesg| grep sd:

[    1.361162] sd 2:0:0:0: [sda] 16777216 512-byte logical blocks: (8.58 GB/8.00 GiB)
[    1.361205] sd 2:0:0:0: [sda] Write Protect is off
[    1.361210] sd 2:0:0:0: [sda] Mode Sense: 61 00 00 00
[    1.361253] sd 2:0:0:0: [sda] Cache data unavailable
[    1.361257] sd 2:0:0:0: [sda] Assuming drive cache: write through
[    1.363223] sd 2:0:0:0: Attached scsi generic sg1 type 0
[    1.363398]  sda: sda1 sda2
[    1.363788] sd 2:0:0:0: [sda] Attached SCSI disk
[    1.364425] sd 2:0:1:0: [sdb] 1572864000 512-byte logical blocks: (805 GB/750 GiB)
[    1.364466] sd 2:0:1:0: [sdb] Write Protect is off
[    1.364471] sd 2:0:1:0: [sdb] Mode Sense: 61 00 00 00
[    1.364512] sd 2:0:1:0: [sdb] Cache data unavailable
[    1.364515] sd 2:0:1:0: [sdb] Assuming drive cache: write through
[    1.370673] sd 2:0:1:0: Attached scsi generic sg2 type 0
[    1.405886]  sdb: unknown partition table
[    1.406228] sd 2:0:1:0: [sdb] Attached SCSI disk
[    4.493214] Installing knfsd (copyright (C) 1996 [email protected]).
[    4.493849] SELinux: initialized (dev nfsd, type nfsd), uses genfs_contexts
[    5.933636] EXT4-fs (sdb): mounted filesystem with ordered data mode. Opts: (null)
[    5.933649] SELinux: initialized (dev sdb, type ext4), uses xattr
[    6.099670] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
[    6.108488] SELinux: initialized (dev sda1, type ext4), uses xattr

Output from fdisk -l

Disk /dev/sda: 8 GiB, 8589934592 bytes, 16777216 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x000dfc09

Device    Boot     Start       End  Blocks  Id System
/dev/sda1 *         2048   1026047  512000  83 Linux
/dev/sda2        1026048  16777215 7875584  8e Linux LVM


Disk /dev/sdb: 750 GiB, 805306368000 bytes, 1572864000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/fedora_dataserv-swap: 820 MiB, 859832320 bytes, 1679360 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/mapper/fedora_dataserv-root: 6.7 GiB, 7201619968 bytes, 14065664 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
linux vmware-esxi

7 Answers

  1. From the information you provide, you have two VM disks:

    • /dev/sda: 8GB with two partitions /dev/sda1 and /dev/sda2

    • /dev/sdb: 750GB with no partition, which should be the one you newly added.

    Your fdisk -l command result shows that you have created a LVM volume called fedora_dataserv and according to the used disk space, you are using the /dev/sda disk only.

    You can refer to the Answer I have posted before, change the value of deb-web138 to fedora_dataserv. For example:

    # vgextend deb-web138 /dev/sdb1
# lvresize -L+70G /dev/deb-web138/root
# resize2fs /dev/deb-web138/root

    are changed to:

    # vgextend fedora_dataserv /dev/sdb1
# lvresize -L+70G /dev/fedora_dataserv/root
# resize2fs /dev/fedora_dataserv/root

    in order to increase the space you can use.

    • 4

  2. If you simply type

    mount

    you will see, which folder is mounted to which disk.

    • 2

  3. lsscsi

    dmesg| grep sd

    cat /proc/scsi/scsi

    fdisk -l

    • 2

  4. sda is the drive connected to the first logical port in your VM's configuration. sdb is the drive connected to the second logical port in your VM's configuration. sda1 and sda2 are two partitions on the first drive, and sdb appears to have no partitions (i.e. is the one you added). You can use gparted or (if formatted as such, lvm) to see how your partitions are laid out.

    • 2

  5. blkid will list the drives. You should be able to identify them based on their sizes, partitions, UUIDs, filesystem types, and so on. lsblk is also quite useful to get a graphical overview of the devices, but doesn't show the filesystem type.

    • 2
  6. Best Answer

    Thanks to everyone who answered. Everyone who did so, helped me track down the issue, and taught me much!

    For some reason, Linux was not recognizing the 2 new drives. (I did not know that until I learned from the others' answers.

    The final solution was:

    1. shut down the vm
    2. Remove the 2 new drives from in the vm in the vSphere client, without deleting them from the datastore
    3. Reboot the vm
    4. Shut down the vm
    5. add one drive in vSphere
    6. reboot the vm
    7. Confirm the os recognizes the new drive (fdisk -l), which it did
    8. Shut down the vm
    9. add the other drive in vSphere
    10. reboot the vm

    fdisk -l now shows /dev/sdc and /dev/sdd

    Thanks again to everyone for the help!

    • 2

  7. /dev/mapper is where mounted luns and LVM partitions are automounted, usually with friendly names.

    If your system uses LVM, man lvm. If you're using mounted luns, check out dm-multipath.

    • 1