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Dynamic Storage Solution

Posted on 2004-04-10
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Last Modified: 2010-05-18
Hi,

Can someone tell me about a good way to create a storage solution with several disks? I want some redundancy like RAID5 so that if a disk fails, data isn't lost and if I have not enough space, it should be possible to add more disks.

If RAID5 is the best way to go, can someone show me the way to a good dummy level tutorial (manual)?

Thanks in advance.
Greetz
Filips
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Question by:Filips
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by:Filips
ID: 10796640
BTW: Working on Redhat ES v3
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by:Karl Heinz Kremer
ID: 10796657
I would suggest that you run LVM on top of a RAID 5 system. This way you have the advantages of a RAID system, butyou can also add more space if you need it: http://www.aplawrence.com/Linux/lvm.html
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by:Karl Heinz Kremer
ID: 10796662
BTW: LVM is the Linux Volume Manager, this HOWTO explains pretty much everything about it: http://www.tldp.org/HOWTO/LVM-HOWTO/
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by:Filips
ID: 10797026
Question: will the to the LVM added disks covered by the RAID5. That is; when I have disk sda, sdb, sdc, sdd and sde in a raid 5 and I add a disk sdf to LVM and afterwards sdf fails and I replace the disk, will the data still be there?

Do I have to use RAID or is LVM alone enough?

Thanks in advance.
Greetz
Filips
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Expert Comment

by:Alf666
ID: 10801410
LVM and RAID a *pretty much* the same things. At least, the same concepts.

RAID stands for Redundant Array of Independent Disks. There are different levels of RAID.

Basically :
- RAID1 is mirroring. This means that you have to use twice the disk space.
- RAID5 is the luxury RAID as it's the level for which parity bits are scattered across all disks. Its a bit expensive in terms of IO (slows the disk access down), but it allows you to "burn" any ONE of the disks, replace it, and rebuild without any data loss.

For more infos, have a look here :

http://www.raidweb.com/whatis.html

Hardware RAID implementations sometimes also allow "hot-swapping". This means that you can take off a disk even if the array is powered up. Thus replacing a disk without stopping the system.

LVM is just a (free) software implementation of different RAIDs. It's slower than a hardware implementation, but implemented in Linux at the kernel level.

So, it's your choice of which RAID you want to implement with LVM. The above suggestion of RAID5 by khkremer is good. You basically spare 1/5 of your disk space, but it's worth it if you need it.

So, to answer your question, all the disks you add to the RAID config will participate in your RAID array. And if ANY one of them fails (one at a time !), you should be able to replace it without any data loss.
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Karl Heinz Kremer earned 500 total points
ID: 10801492
LVM and RAID are two completely different things. Some of the use cases to overlap, but in general we are talking about two different things. LVM allows you to combine different physical disks into a logical volume, you can add new disks when you run out of space, or take disks out of your volume group if you don't need it anymore. LVM does not provide any redundant data storage, which RAID does. With RAID your primary objective is to fault tolerant  data storage. You can run LVM on top of a RAID system (see my first link) if you need fault tolerant storage plus easy volume management.
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Expert Comment

by:Alf666
ID: 10801547
Hem... Please ignore my whole comment. I mixed up lvm with md :-(

I'm going back to bed. Flu and computers don't mix so well...
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by:Filips
ID: 10802846
Alf666, get better soon. I need you here.
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