Raid array showing only the capacity of one disk

Question

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.

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 03 '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 03 '12 at 23:23
In that case, read the link I posted again. Depending on how high traffic your site is you might want to change the RAID level to something which suits you better. This is something you want to do before installing lots of software. — Hennes, Aug 03 '12 at 23:24
I see, I need storage but I dont want to loose any data, I want something like 100GB on raid1 to store my website, the OS and all that stuff, and 900GB (1800GB) on raid0 to store only videos, but I supose I'll have to repartition the disks. — Shixons, Aug 03 '12 at 23:45
@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 04 '12 at 05:30

score 6 · Accepted Answer · answered Aug 03 '12 at 23:13

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?.

score 4 · Answer 2 · answered Aug 03 '12 at 23:12

4

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

answered Aug 03 '12 at 23:12

jamieb

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Raid array showing only the capacity of one disk

2 Answers2