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Old 11-21-2003, 12:16 PM   #1
gte704p
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Software RAID - on one partitioned drive


I have a 36 Gig drive that we are using as our system disk. I need to set things up so that I can create a mirror of this drive by using software raid and partitioning the drive.

In other words, half of the drive will be the active OS and the other half will be its mirror.

Does anyone know if this is possible with Software RAID? and if so how... or where do I find the information to accomplish it?

Thanks.
 
Old 11-21-2003, 12:38 PM   #2
artur
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It is possible, but Not A Good Idea. It will drasticly increase wear on your drive and slow down your disk transfers as the read/write heads will have to jump between both partitions continuously for every single byte you access. (Well, ok, not exactly, because there's caching on the HD and in the drivers, etc... but this is mostly correct).

You're MUCH better off adding a second drive or at least writing a cron script that either uses dd to mirror one partition to the other or uses rsync to sync files on them periodically.
 
Old 11-21-2003, 01:08 PM   #3
gte704p
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Unfortunately money is the limiting factor in not adding another disk... so that option was crossed out by sources higher than me.

RAID however is the direction I would like to take. Do you have or know of any resources which would help me out? I am not overly concerned with the wear on the drive, and I am more concerned with attempting and testing this type of configuration.

Thanks.
 
Old 11-21-2003, 01:55 PM   #4
artur
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Quote:
Originally posted by gte704p
RAID however is the direction I would like to take. Do you have or know of any resources which would help me out? I am not overly concerned with the wear on the drive, and I am more concerned with attempting and testing this type of configuration.
I'd recommend reading the RAID-howto. Can be found on www.tldp.org I think there's a mention in it about using multiple partitions on one drive.

If money is a concern, I'd be concerned with wear on the drive. You may end up having to buy one anyway and sooner than you think... Besides, what's more valuable - the cost of extra drive or the data that's stored on it? Just a few thoughts to consider or use as arguments with the decision makers...

Good luck with your experiment.
 
Old 11-21-2003, 02:10 PM   #5
gte704p
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Thanks for the help.

Maybe if I can get a drive to fail they will realize that money is going to be spent either way.
 
Old 11-21-2003, 02:46 PM   #6
Electro
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You can use two 20 gigabyte hard drives. Then setup them as RAID 1 using LINUX built in RAID.

dd only works if the drive is unmounted.
 
Old 11-22-2003, 04:24 AM   #7
mcleodnine
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Don't use software RAID on a single drive. It's pointless, risky, and gives you no redundancy. If the drive fails it doesn't really matter if you have data on two partitions and, as Atrur already pointed out, all that extra thrashing is sure to increase the failure rate.

Hardware and software RAID1 is a solution meant to reduce data loss due to hardware failure, and won't do much for you when someone does a 'rm -rf /' or other ghastly mistakes. RAIDx is not a backup medium and shouldn't be treated as such.

While we're on the topic - don't use master/slave drive setups in a software RAID array.

If you need some assurance of availability you should invest in another drive.

If you need some redundancy for accidental data loss there are backup tools ranging from the simple (faubackup) to more complex tools like amanda. If you're really paranoid you can set it up so that it unmounts the backup device to reduce exposure to user error.
 
  


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