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

[Nick B]

RAID 5 (or 6, or 4, or any cpu intensive raid) on a FusionIO card is a very
bad idea.
Nick


On Thu, Nov 7, 2013 at 2:11 PM, Patrick Giagnocavo <patrick at zill.net> wrote:

> 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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