[SOLVED]Raid, lvm or sth else? Need advice :)

Yatmai · Veteran Joined: 12 Nov 2005 Posts: 1501 Location: Kraków

I want to create one huge storage from 2 partitions - each of diffrent hdd. I know, I can use raid0, raid linear or lvm, but which method will allow me to recover any data from partition A, when part B fails?

I don't want to recover all - some data from that storage will be on disc A, and some on B. Then if ie. B fail (Tux bless out storages

) I would like to recover data which was on disc A.

Is there any method, which allows that?
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mgrela · Posted: Mon Jan 19, 2009 10:15 am Post subject:

Neither LVM nor RAID won't help you achieve the result you want. LVM only combines block devices into larger ones so when one of your drives fails you will loose half of your filesystem. On the other hand, havin RAID with only two drives doesn't make much sense. Just create a filesystem on each hdd and mount them as subdirectories of a common mountpoint, ie. /mnt/storage/hdd0 and /mnt/storage/hdd1.

br,
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dirk_salewski

Yatmai · Veteran Joined: 12 Nov 2005 Posts: 1501 Location: Kraków

I know, but I already have raid1 matrix for most important data

The storage, I was talking about is about 400GB, so 50% lost from this would be too much.
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fangorn · Veteran Joined: 31 Jul 2004 Posts: 1886

You have some options then

Easiest: as mgrela already wrote, mount them into subdirectories and do the splitting yourself.

or: buy another drive and do RAID5 (will loose you the capacity of the new drive only)

or: buy a drive big enough to hold all the data and do RAID0 (or LVM for that matter) with regular backups.

The backup is advisable anyway, regardless if you choose LVM, RAID0, RAID5 or two mountpoints. The best RAID can only protect you from failing hardware. Not from errouneous software, user-malfunction :twisted:

or other possible reasons for lost data.
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mgrela · Posted: Mon Jan 19, 2009 2:06 pm Post subject:

Have you seen mhddfs ?
http://debaday.debian.net/2008/05/25/mhddfs-join-several-real-filesystems-together-to-form-a-single-larger-one/
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Maciej Grela
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Yatmai · Veteran Joined: 12 Nov 2005 Posts: 1501 Location: Kraków

mgrela · Posted: Mon Jan 19, 2009 7:45 pm Post subject:

Your benchmarks seem to be very promising

. I thought, that a fuse solution would be much slower. But then maybe it is time to move out all the filesystems from the kernel to userspace

. Now I'm almost certain I will use mhddfs on my own storage box when I spare some time to build one.

br,
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Maciej Grela
You just keep on trying till you run out of cake.

szczerb · Posted: Mon Jan 19, 2009 8:04 pm Post subject:

In case someone didn't find this already, here is a pretty fresh (3 days old) ebuild:
https://bugs.gentoo.org/show_bug.cgi?id=220451

beandog · Posted: Tue Jan 20, 2009 12:23 am Post subject:

Oh man, this is super awesome ... I can't wait to do some testing on this.

I've been looking for a solution to form one directory out of multiple USB drives. LVM/RAID obviously wouldn't be a solution, but I'm willing to bet this could take it to task.
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