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Marco Marsala
Asked: 2015-10-14 12:35:34 +0800 CST

Why third partition of /dev/sda is shown as /dev/sdb instead of /dev/sda3?

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I have two 3 TB disks in hardware RAID-1 (mirroring), controller DELL PERC H310 (it is a Dell PowerEdge R420 server).

I have three partitions on the same disk.

df and fdisk commands shows the third partition as /dev/sdb instead of /dev/sda3.

I cannot understand why works in this way.

[root@ru000397 ~]# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        91G  5.6G   81G   7% /
tmpfs           7.8G     0  7.8G   0% /dev/shm
/dev/sdb        2.6T   17G  2.5T   1% /usr/local/psa

[root@ru000397 ~]# fdisk -l

Disk /dev/sda: 107.4 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0b14c924

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1       12035    96664576   83  Linux
/dev/sda2           12035       13055     8190976   82  Linux swap / Solaris

Disk /dev/sdb: 2892.7 GB, 2892660473856 bytes
255 heads, 63 sectors/track, 351679 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
fdisk

1 Answers

  1. Sounds like your 3 TB drives are split into two separate LUNs or Virtual Disks, a smaller one for boot, and the rest for your plesk data. It appears the OS you chose doesn't support 2TB+ as a boot volume (which isn't necessarily a bad thing)

    Follow the comments to confirm this in your PERC raid utility at boot (CTRL+R). If you didn't confirm your raid configuration from factory, this is exactly what I would expect.

    If you want to boot 2TB+ you'll need UEFI and a supported OS with GPT.

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