RAID 0 to Raid 1 CentOS 5.4

shaunwingin
shaunwingin used Ask the Experts™
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Say, I wish to change the RAID version. I have a DVD RW drive. What detailed steps are needed to burn image and restore. We are talking 3x250GB hard disks in RAID 0, however only the CENTOS OS is loaded? Can I copy the Image over a the network to another machine in place of to the DVD RW?
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Commented:
Btw Its a hardware RAID - HP Proliant ML110 G5

Commented:
If your imaging software supports network/lan communication then you should be able to image the RAID to a remote computer file, and it should support restoring the image from the network/LAN.
Any idea of the actual used space on the 750GB array?  It the space usage is really small then a DVD RW may be OK to try.  My preference would be to install another drive into the machine and make an image via disk to disk

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Commented:
Tx, but I need detailed steps to to burn image and restore using Linux opensource software or Bash commands please.
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Commented:
First use Gparted to reduce the partition sizes so they will fit to the new RAID 1. I recommend PartedMagic for this:

http://partedmagic.com/

You could use paragon's free backup tool which you can make a CD of (just first install it to a windoze PC, then start the utility and it'll have an option under "Tools", "Recovery Media Builder" to make a booting CD with the tool on it (I think it even uses Linux for the CD).

http://www.paragon-software.com/free/db.html

After that boot the Server with that CD, and you'll see a network configuration option, where you can map the network drive to which you want to backup to, and then you can just use it to make your backup (it recognizes Linux partitions, so that is nothing to worry about). Then just kill your array and build the new one, and again use the utility to restore your image.
Daniel McAllisterPresident, IT4SOHO, LLC

Commented:
Well now... here is a good example of why you need to keep extra hard drives around!

For the benefit of future readers:
===========
  RAID-0 stripes (spreads) data across all drives in the array element. The desired effect is to create larger "virtual" drives and improved performance. The problem is that the failure of any 1 component (drive) results in a complete data loss.
  RAID-1 mirrors (copies) data across two drives in an array element. (NOTE: a 3rd or even 4th copy is legal, but seldom used). The desired effect is data protection. The problem is that you pay double for storage. This USED to be a big problem, but with 2TB drives costing under $200 each, the cost factor just doesn't hold water much anymore.

The other common RAID types are 3 & 5:
  RAID-3 stripes data across all-but-one of the drives in the array element. The "other" drive is called a "parity" drive. It is used for data protection (and re-building) if (when) a component failure occurs. It works very much like the modem parity everyone knew (and loved) back in the dial-up internet access days. The desired effect is to create larger "virtual" drives (like RAID-0), but without the risk involved, since the parity drive allows for "reconstruction" of a failed component. The problem is that every disk write has to have an effect on the applicable data drive AND the parity drive... the latter (parity drive) becomes a bottleneck that prevents the performance enhancements you might expect with the other striping.
  RAID-5 is similar in concept to RAID-4, but it attempts to compensate for the parity drive bottleneck by spreading the parity across the components. (Say, for track 1 the parity disk is drive 0, for track 2 it's drive 1, and so on). This became a very popular array type while storage was still relatively expensive (and since SCSI drives are still expensive -- I don't know why it's still more than $1/GB for SCSI storage -- RAID-5 is still common in SCSI arrays).

There are lots of other RAID forms -- with RAID-10 becoming rather popular -- and I've glossed over a LOT of details (like how RAID-3 and RAID-5 are really more different than I've pointed out)... if you want to know more, look here:
  http://en.wikipedia.org/wiki/RAID
============

So now, on to the problem.... you have your data spread across 3 250GB drives (750GB total storage) and you want to "fix" this to become RAID-1 storage (250GB total storage with an extra 250GB drive laying around somewhere.

The key issue is, as you have pointed out, you need some kind of "extra" storage to hold your data while you fiddle with the drive layouts!

First things first -- if it were me, I would spend the $50 -to- $100 bucks for a 4th 250GB drive, back up my data to it (I prefer the old UNIX standby: dump as a backup tool), then build a 500GB RAID-10 array (or two separate 250GB RAID-1 arrays).

But if we assume you don't have such a thing available, and are limited to the resources available, then there are some problems to overcome:
 1) Just to get this out of the way: There are no tools that will simply re-organize the files on your 3 drives into a RAID-1 array in any single or easy set of steps. They don't exist, and wouldn't be worth much if they did -- too risky to be worth the effort, really...
 2) to burn a DVD (or set of DVDs) to recover from, we'll need to make images of the drives... and there's the rub -- we need to STORE the images on the very filesystem we are taking an image of!

So, regardless of the approach, you will need to follow these basic steps:
 1) backup the data (to a hard drive, DVD or set of DVDs, or onto another system altogether)
 2) Trash your RAID-0 array & build your RAID-1 array (this will render the drives effectively empty)
 3) Perform a "basic" Linux install on the RAID-1 array just so you can get booted
 4) "Recover" using your backup from step 1

Each step will have its gotchas depending upon what decisions you make throughout -- so if you could be specific about the other hardware you have available and the amount of data we're talking about, I can guide you through without writing a book series on how to do this in the general case.

Let's start with how much data there is (try df -h) & what media you have available to store the backups to...

Dan
IT4SOHO

Author

Commented:
Tx 4 the detailed info. I don't have a spare drive at moment.
There is a DVD writer so this looks simplest way to copy data.

Btw, Can I convert Raid 1 to Raid 10 easily? and
Btw Its a hardware RAID - HP Proliant ML110 G5

[root@localhost ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      675G  2.9G  637G   1% /
/dev/mapper/ddf1_A1Server1p1
                       99M   18M   76M  20% /boot
tmpfs                 505M     0  505M   0% /dev/shm
[root@localhost ~]#
Daniel McAllisterPresident, IT4SOHO, LLC
Commented:
The hardware/software nature of the RAID isn't material... but you raise an excellent possibility.

Regardless of whether it is hardware or software RAID-0, the issue is that all your harddrives are "occupied" in a manner by which the removal of any one of them destroys your data.

But you asked about converting from RAID1 to RAID-10.... if your RAID card held more disks, you could have done the OPPOSITE -- converted your RAID-0 array to a RAID 0+1 array (by adding 3 more 750GB drives!)

But, alas, the HP Proliant ML110 G5 comes with only a 4-drive RAID controller. But the answer to your question is YES... once you have established the RAID-1 array on the RAID controller, you should then be able to make it a RAID 10 array by adding 2 more disks.

I say SHOULD -- that is a not-so-simple conversion (but, unlike the RAID-0 to RAID-1 conversion you started off wanting to do, not a DANGEROUS one, and not an overly difficult one). However, your RAID controller very well may not support this, so I'm afraid that this is a prime opportunity to RTFM (read the fine manual).

Either way (if it will do it for you or not), you'll need a 4th identical drive to make RAID-10 work.... and if that is your eventual goal, perhaps you would do best to await the new drive to use IT as the "backup" drive. Burning a DVD image is likely to be more difficult than you think!

Good Luck!

Dan
IT4SOHO

PS: One more tool you might find handy for the "dump" (backup of the current RAID-0).... read up on "rdump" -- which should let you do a "level 0" dump across a network -- thus, allowing a local Windoze system (or other Linux system) to lend its storage to your backup quest.

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