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I've a dedicated server with an raid array with two disks of 1TB each, this is what I get with mdadm --detail /dev/md1

/dev/md1:
    Version : 1.1
Creation Time : Wed Aug  1 20:20:14 2012
Raid Level : raid1
Array Size : 975186812 (930.01 GiB 998.59 GB)
Used Dev Size : 975186812 (930.01 GiB 998.59 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Intent Bitmap : Internal

Update Time : Sat Aug  4 00:50:31 2012
      State : active 
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

       Name : xxxxxxxxxxxxx
       UUID : xxxxxxxxxxxxx
     Events : 4843

Number   Major   Minor   RaidDevice State
   0       8        3        0      active sync   /dev/sda3
   1       8       19        1      active sync   /dev/sdb3`

But I see the array with only 1TB and not the 2TB of both disks.

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  • 2
    Is this serious?
    – MDMarra
    Aug 3, 2012 at 23:16
  • Sorry I've never used linux before, how should I know this?
    – Shixons
    Aug 3, 2012 at 23:18
  • 3
    Yes. Because it is not Linux specific. RAID1 (or RAID5/6) setup of discs is very common in servers and both allow the server to keep operating if a disc has failed. This is essential to most corporate servers. A single disc failure should not result in problems for potentially hundred of people. And in reverse, how RAID and how backups work it something each admin should know. (Sorry if I sound harsh)
    – Hennes
    Aug 3, 2012 at 23:21
  • Yes but I'm not a server admin, I'm just a webmaster with a high traffic website wich need a dedicated server.
    – Shixons
    Aug 3, 2012 at 23:23
  • 2
    @Shixons: If you're not a sysadmin, this isn't the right site for you. As per the FAQ, Server Fault is a community for professional systems administrators.
    – womble ♦
    Aug 4, 2012 at 5:30

2 Answers 2

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6

From your post: Raid Level : raid1.

Two 1TB drives in a RAID 1 are supposed to yield 1TB of usable space. Everything is working as expected.

Think of your hard disks as books. To prevent loss of information (e.g. in case of a coffee spill) you write all your information to two books. Now your have two books but still only room for one book of entries.

For a bit more professional and a much longer answer check out this post: SF: Canonical question: What are the different widely used RAID levels and when should I consider them?.

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4

RAID1 is mirroring. You're only going to get the usable capacity of one disk.

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