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Re: Moving from RAID 0 to LVM RAID?

 On Thu, 2008-03-06 at 23:49 -0500, Ben Holland wrote: 
> >> this is bad and in fact your LVM controller may really 
> >> hate you 
> >Um... There is no such thing as an LVM controller. Its all done in 
> >software by the kernel. 
> Recovery from a broken disk, I would say depending on the drive condition 
> but over all when i've seen drives die they die hard, some of the data is 
> recoverable I'm sure but not all. 

I believe both Tom and I were referring to recovery of data from a 
logical volume that spanned multiple physical disks. i.e., LVM is more 
like JBOD than RAID, where files are usually constrained to one disk or 
another, so files on the non-dead drives are completely intact and 
easily recoverable. 

> And the controller I was talking about is 
> the kernel module, obviously it's not in hardware. Perhaps I'm using the 
> wrong word, I've always referred to the thing that governs the LVM's as the 
> lvm controller. 

Ah, okay. I think scsi controller -> hardware, raid controller -> 
hardware, sata controller -> hardware, etc., so an 'lvm controller' 
logically follows as a piece of hardware too. 

> LVM's  I would say are kinda neat, but to be honest I still 
> haven't seen a case where they were needed. 

Me neither. They annoy me, and I don't use 'em most of the time. 

> >I'd wager more like 50-50. I've seen plenty of 2U boxes that have 4 to 6 
> >drive bays and don't come with any RAID controller at all, let alone one 
> >capable of RAID 5. 
> I'm very surprised by this. Every low end rack comp i've seen that wasn't 
> more then 3 years old has come with some form of raid, to the point where I 
> can even get hardware raid on MB's for personal home comps. 

You sure that's actually hardware RAID you're talking about, and not the 
crappy bios-driven pseudo-raid, which is really just glorified software 
RAID (with all the drawbacks and none of the benefits of linux kernel 
software RAID)? 

> There were a 
> bunch i've worked with that were true POS in every sense of the word, but 
> they were EOL and their replacements had raid on board. Every single 4-6 HDD 
> comp i've seen I think i've seen a built in raid controller capable of 
> handling 5. If not then I highly recommend getting boxes that do in fact 
> have hardware raid, if you can't then use software. 

Lots of low-end rack hardware from the likes of both Dell and HP (the 
bulk of what we have in our lab) come with nothing but SATA controllers 
that only do bios pseudo-raid, unless you opt for upgrades. 

Jarod Wilson 
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