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Re: [K12OSN] Raid Level Choice



Les Mikesell wrote:

On Wed, 2004-12-22 at 13:38, Burke Almquist wrote:



LVM lets you combine physical volumes so you get the same effect
as RAID0.


LVM gives you the space benefits but not the speed benefits of using RAID 0 since it doesn't "stripe" the data across disks. (Assuming that most of your writes occur to the same partition, /home say)



I think your files have to be large enough to span across disks (i.e.
more than one cylinder) before you would see a speed benefit from
the RAID0 stripe effect. And the benefit you get from the head on
the 2nd drive being in the right place to continue reading comes
at the cost of it not being in the right place for a file someone
else wants at the same time. I'm not sure how LVM handles the
separate devices but in general for multiuser use you want as
many independently-seeking heads as you can get because disk head
motion is the slowest computer operation. RAID tends to lock them
all together.


---
 Les Mikesell
  les futuresource com


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so are you saying there is basically no advantage to hardware raid?

I have effectively shot my wad getting the 4 drives and the raid controller. I was intending it to be both increasing capacity and giving the system some sense of disaster recovery through raids ability to rebuid or work with alternate mirrored drives

The setup I am currently using has less than 30 GB of hard drive space, all of it slow, 5400 rpm old scsi drives. The faster newer larger SATA drives should give me at least the equal to it performance wise. I can function now, I am just out of space and suspecting a drive of being on the verge of failure. each new drive is 80 GB in size, so even in something like raid 10 I am getting 160 GB usable space, right? over 5 times what I have now. with raid 5 I would have even more.

What I am looking to do is acheive a perfomance increase, however slight, while insuring a better disaster recovery. Right now I got nothing except I xcopy the /home directories to my laptops hard drive via samba share. In other words, anything is an improvement over that. the controller I bought does hardware raid, so why wouldn;t I use that instead of software raid via lvm, which in itself has a performance hit, right? I just don;t know for sure whether to do 5 or 10. People tell me 5 is better, disaster recovery wise, but with a performance hit. 10 is faster, but no parity stuff is happening, so less disaster recovery


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