[BBLISA] Moving from RAID 0 to LVM RAID?

[Andrew Cohen]

Hardware vs Software RAID?  That's a no-brainer.  Do it in hardware, let
the computer CPU work on more important things.

 

PE2950: Doesn't come by default with the PERC.  You have to specify it
when ordering.  It's possible, though doubtful, that the server in
question does not have the hardware RAID card in it.

 

From: bblisa-bounces at bblisa.org [mailto:bblisa-bounces at bblisa.org] On
Behalf Of Edward Ned Harvey
Sent: Friday, March 07, 2008 8:16 AM
To: bblisa at bblisa.org
Subject: RE: [BBLISA] Moving from RAID 0 to LVM RAID?

 

Yeah, that's right - 

 

You did say PE 2950, and you also said raid controller only supports 0
or 1.  This is almost certainly false.  You have the PERC 4, 5, or 6,
right?  These all support Raid 5.  Which is a clear choice over 0.

 

 

 

 

From: bblisa-bounces at bblisa.org [mailto:bblisa-bounces at bblisa.org] On
Behalf Of Rick Pike
Sent: Thursday, March 06, 2008 11:41 PM
To: bblisa at bblisa.org
Subject: Re: [BBLISA] Moving from RAID 0 to LVM RAID?

 

You didn't give much detail about the hardware, but you mentioned a
PE2950 which I assume is Dell Power Edge 2950. I worked with some of
these last year and our standard storage configuration was 4 internal
disks configured as a single RAID 5 volume using the embedded RAID
controller. Actually what I had recommended was 6 smaller internal disks
for the same price.

The RAID 5 provided an acceptable balance between capacity, protection,
and performance. We did some minimal testing to see if reconfiguring the
same hardware with mirroring (was it 2 RAID 1 volumes or 1 RAID 1+0
volume?)  would provide a performance boost (at the expense of
capacity), but we did not notice an meaningful difference in our
application. Your mileage may vary.

Rick

On Thu, Mar 6, 2008 at 6:58 PM, Scott R. Ehrlich <scott at mit.edu> wrote:

So I've learned a valuable RAID 0 lesson, and it fortunately was not a
major
catastrophy.  I got lucky, and had a workable-enough backup on tape to
make the
user who needed some data happy.

Now, from the OS side, LVM is an option.   Say the RAID controller only
allows
hardware striping or mirroring for logical volumes, but I want to use
more than
two disks, and I don't want the RAID 0 problem again.

When I get a replacement disk and build the system from the ground up
again, I
could, conceivably, use hardware RAID 1 for the OS on two disks, and
CentOS 5
64-bit's LVM for software RAID 5 (or maybe 1+0 if available) on the
remaining
for 4 disks, maybe 3 disks as active and the 4th as a hot spare?

I've never had much faith in software raid, since it is not
hardware-based, and
there would be a performance hit, but in this case, it could be an
option.

Insights from the OS-created RAID experience welcome.

Thanks again.

Scott

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