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 okir@monad.swb.de).
[    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

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.


If you simply type


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

  • Cool. Thanks. I see no mention of sda. That should be my os drive, right? There is also no mention of sda2. sda1 has - /dev/sda1 on /boot type ext4 (rw,relatime,seclabel,data=ordered) . So, I still cannot tell which is which. I should have 2 drives that are unformatted with no filesystem. – Roger Creasy Aug 12 '16 at 13:28


dmesg| grep sd

cat /proc/scsi/scsi

fdisk -l

  • I added the results of dmesg | grep sd I don't know how to read them :-) – Roger Creasy Aug 12 '16 at 13:44

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.

  • 1
    OK. Does that mean that Linux is not finding the other 2 drives (the last 2 that I added) at all? If it is not finding them, how do I resolve that issue? I do see that sdb IS mounted. – Roger Creasy Aug 12 '16 at 15:54
  • Try ls /dev/sd* and see what you have; if all four drives were detected, you should probably have sda, sdb, sdc, and sdd. Partitions that are detected will be numbered; the prefix is "physical" (virtual) drive, and the numbered values are the partitions. – phyrfox Aug 12 '16 at 15:58
  • I have /dev/sda , /dev/sda1, /dev/sda2, and /dev/sdb. I do not have sdc or sdd – Roger Creasy Aug 12 '16 at 16:00
  • @RogerCreasy What's your output from fdisk -l? – phyrfox Aug 12 '16 at 16:14
  • I added the results to my question – Roger Creasy Aug 12 '16 at 16:18

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.


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!

  • You can actually detect new drives at runtime with scsitools. You can then run rescan-scsi-bus as root. – mzhaase Sep 9 '16 at 15:28

/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.

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