[geeks] RAID0+1 and ideas, etc...

[Patrick Giagnocavo]

There are a few questions:

1.  Do you "need" LVM?  Personally I find it slow, but the ability to make a snapshot so you can backup stuff is nice and mostly works.

2. You can create, using 6 drives, a single large but redundant device which you then put ext4, xfs, etc. on top of, with just MD devices.  RAID10 (capacity of 3 devices)  or RAID6 (capacity of 4 devices) would work.

3. You can test using ZFS.  I would create a ZFS raidz2, I think (giving me the capacity of 4 drives) then, use "zfs send" to backup in near realtime or on your chosen schedule to spinning rust.  The reason to use z2 instead of raidz is that if a controller goes, you lose 2 devices, not 1.

Certain operations in Linux' ZFS are slower than I would like, but that might not matter - depends on exactly what you are doing.  

The ability to set the recordsize (if for example you are using a database with a particular recordsize) might be an advantage; as well, I would ask whether the FusionIO devices have built in ECC or not, to ensure that what is written and then read back, is always consistent (it is after all a new technology).

Hope this helps.

----- Original Message -----
From: "Jonathan Katz" <jon at jonworld.com>
To: "The Geeks List" <geeks at sunhelp.org>
Sent: Thursday, November 7, 2013 9:12:56 AM GMT -07:00 US/Canada Mountain
Subject: [geeks] RAID0+1 and ideas, etc...

All,

Say you're running a Linux server. It has six Fusion IO cards, each
presents two disk devices giving you a total of 12 disk devices. You
want to RAID 1+0 this setup so that if any physical card or disk
device dies, you're still operational.

My customer set this up using mdraid to stripe the two disk devices
within the individual cards. So we go from 12 disk devices to six md
stripes. Then the md stripes are mirrored card-by-card (so there are 3
md mirror/RAID1 devices.) Then LVM is used to stripe the three
remaining cards into one large volume that we use.

I'm not sure this is the best way to do it, and I want to hear from
others who deal with this what they think (which is why I'm throwing
this out there.) The requirement is for one decent sized, reliable
storage pool of data. I think we have an extra layer of abstraction
here, but I'm not sure how to redo this, or if we even should.

What say the mind trust?

-- 
-Jon
Jonathan Katz, Indianapolis, IN.
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