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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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closed as not constructive by John Gardeniers, womble, Scott Pack, Tim Brigham, Ward Aug 24 '12 at 3:50

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2  
Is this serious? –  MDMarra Aug 3 '12 at 23:16
    
Sorry I've never used linux before, how should I know this? –  Shixons Aug 3 '12 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 '12 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 '12 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 '12 at 5:30
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2 Answers 2

up vote 6 down vote accepted

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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Thank you, I understand now. –  Shixons Aug 3 '12 at 23:18
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RAID1 is mirroring. You're only going to get the usable capacity of one disk.

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