[BBLISA] Moving from RAID 0 to LVM RAID?

[Daniel Feenberg]

On Thu, 6 Mar 2008, Edward Ned Harvey wrote:

> In nearly all situations, I'll recommend hardware raid controller, with
> hotswappable hard drives, and at least raid 5 configuration.  So you get the
> performance & size benefit of a bunch of disks, with at least some
> redundancy to prevent data loss during hardware failure.
>

My worry about hardware RAID controllers is what if it breaks? Would you 
need to replace it with the same make, model, and firmware rev level to 
recover your data? Or is there some compatibility across models within a 
brand? We have several RAID controllers from 3Ware and RocketRaid, none 
make any such claim in their documentation or online. Nor have I ever seen 
any software that claimed to be able to recover data from hardware raid 
arrays without the hardware.

Anyway, with multi-core processors, the CPU load from software raid is not 
very important.

In case anyone on this list hasn't seen it, I posted some lessons we have 
learned about storage at

  http://www.nber.org/sys-admin/linux-nas-raid.html

Daniel Feenberg


>
>
>> -----Original Message-----
>> From: bblisa-bounces at bblisa.org [mailto:bblisa-bounces at bblisa.org] On
>> Behalf Of Scott R. Ehrlich
>> Sent: Thursday, March 06, 2008 6:58 PM
>> To: bblisa at bblisa.org
>> Subject: [BBLISA] Moving from RAID 0 to LVM RAID?
>>
>> 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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