Linux software RAID - o wat

RedVenom

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On the off-chance that anyone happens to know a lot about this, here's the problem...

I want to create a dynamically expandable raid5 array over my 3x200gb disk set with a seperate system disk. I've read up everywhere I can on both volume management tools (LVM) and raidtools to see if this is possible, but I've come to a somewhat sad conclusion - and this I suppose is what I want confirmed. I either......

1) ...create a dynamic volume group under LVM, which I can add and remove new disks from whilst retaining my raid0 stripe. This however isn't resilient.

2) ...take my JBOD and use raidtools to make a normal raid5 set, which isn't expandable without flattening the entire filesystem and re-creating it every time I add a new disk.

Is this right? Is there some amazing way I can botch LVM to sit underneath and add news disks to the LG - and kazam! raidtools will start using it as part of its array? Or are there other tools I don't know about that'll somehow magically do what I'm looking for, other than haivng to shell out for a stupid raid5 IDE adapter?

he;lp.
 

Gurnox

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RedVenom said:
On the off-chance that anyone happens to know a lot about this, here's the problem...

I want to create a dynamically expandable raid5 array over my 3x200gb disk set with a seperate system disk. I've read up everywhere I can on both volume management tools (LVM) and raidtools to see if this is possible, but I've come to a somewhat sad conclusion - and this I suppose is what I want confirmed. I either......

1) ...create a dynamic volume group under LVM, which I can add and remove new disks from whilst retaining my raid0 stripe. This however isn't resilient.

2) ...take my JBOD and use raidtools to make a normal raid5 set, which isn't expandable without flattening the entire filesystem and re-creating it every time I add a new disk.

Is this right? Is there some amazing way I can botch LVM to sit underneath and add news disks to the LG - and kazam! raidtools will start using it as part of its array? Or are there other tools I don't know about that'll somehow magically do what I'm looking for, other than haivng to shell out for a stupid raid5 IDE adapter?

he;lp.
You're spot on I'm afraid. Such things are, as far as I know, beyond the scope of LVM. You can stripe LVM volumes but that's about it.
 

Danya

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Raid 5 is really slow in software anyway, if you're serious about using it, get a decent adapter.
 

Panda On Smack

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\\edit - *snip* - that was a little unnecessary and quite unhelpful Panda. - Xav
 

RedVenom

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Panda On Smack said:
\\edit - *snip* - that was a little unnecessary and quite unhelpful Panda. - Xav
:rolleyes: Jon :rolleyes:

Danya said:
Raid 5 is really slow in software anyway, if you're serious about using it, get a decent adapter.
Thanks for the completely unverified comment.
 

TdC

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can you not make r5 disks with your volume manager?
in something like veritas it would be vxassist -g <diskgroup> make <diskname> <size> layout=<layout> where layout can be stripe, mirror, raidX etc.
sorry I can't be more helpful, I'm not clued in to linux volume managers.
 

RedVenom

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TdC said:
can you not make r5 disks with your volume manager?
in something like veritas it would be vxassist -g <diskgroup> make <diskname> <size> layout=<layout> where layout can be stripe, mirror, raidX etc.
sorry I can't be more helpful, I'm not clued in to linux volume managers.
Apparently LVM doesn't support Raid5 - I can do this in raidtools, but it appears I can't do this in a dynamic manner; eg, adding and removing disks without flattening the entire thing :(
 

TdC

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are you bound to linux? FreeBSD's Vinum volume manage seems to allow raid 5 and much more. look here for info
 

RedVenom

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TdC said:
are you bound to linux? FreeBSD's Vinum volume manage seems to allow raid 5 and much more. look here for info
No, I'm not bound to any distribution - just that I'm not very good at *nix so was using the one I knew best (RH9). However, I'll certainly take a look at what other variants can offer. Cheers.

Do you know if Vinum supports 'dynamically' adding new drives to an existing array without destroying and/or flattening it? Even its website doesn't say much...
 

TdC

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I'm not entirely sure as I've never used it. Perhaps Xane knows? It should though, a VM's not much use if it can't imo. Make volume X, add drives to it, manipulate them. Be aware that if you grow a drive it's filesystem won't grow with it heh.
 

RedVenom

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TdC said:
Make volume X, add drives to it, manipulate them. Be aware that if you grow a drive it's filesystem won't grow with it heh.
This is rather the crux of the situation though, isn't it. LVM does this, and expands the logical volume but doesn't support the level of raid I want. Everything else seems to do the whole raid5 thing, but won't expand it on the fly. Anyone would think I'm asking the world :rolleyes:
 

Danya

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RedVenom said:
Thanks for the completely unverified comment.
You know what google is right? :p

Anyway, consider this graph with hardware raid cards:

Now consider that software raid is more expensive in terms of cpu. That's on a p4 2.26G btw. :p
 

RedVenom

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Danya said:
You know what google is right? :p

Anyway, consider this graph with hardware raid cards:
[img tech report]
Now consider that software raid is more expensive in terms of cpu. That's on a p4 2.26G btw. :p

That doesn't actually compare anything now, does it? Here's another picture to compare the different types of RAID:

 

TdC

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RedVenom said:
Anyone would think I'm asking the world :rolleyes:

hehe indeed. It does seem to be a pain to implement. I'm afraid you'll get either-or, unless you're willing to shell out for something like Veritas (you don't want to, trust me). Sorry I couldn't point you to instant gratification.

Danya - hardware raid solutions, nice as they are, do not provide anything like the level of flexibility that software raid can. it's not even the same ballpark (to quote PF)
 

lovedaddy

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Sadly, I think the answer is going to be no. LVM allows resizing of volumes without destruction of the data, but no redundancy as far as I'm aware.
LVM2 or EVM (i think it is), might be worth a look.

I was looking to create an array a little while back for my house, and eventually came to:
5 * 250 gig Maxtor drives (Maxline II, 5400 spin, I was concerned with heat)
Amd 700 + 256 SDRam
2 * 9.1 gig SCSI (boot/OS, gentoo linux, mirrored)

Installed Gentoo, and the Raid tools. Setup a Raid5 software array, with ReiserFS as the file system.
Gives me about 935 gigs of storage, with 1/4 redundancy.

If I want to increase storage, it will require a backup and restore, sadly. But I really didn't feel comfortable with a terras worth of data being left to the manufacturing promices of Maxtor and their enterprise drives.

With a minimal install, the AMD700 seems to cope with the load of Raid5, I'm happy with the end result (well, bar the fact that its almost full now ;-)
 

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