[BBLISA] Moving from RAID 0 to LVM RAID?

[Edward Ned Harvey]

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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