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

[Sandwich Maker]

" From: Nick B <nick at pelagiris.org>
" 
" Fusionio says "Don't mirror our cards, it's dumb", and in most cases they
" are right.

a guess - they have firmware support for mirroring, offloading the
host?

" Fairly frequently trying to mirror fusionio cards will result
" in a significant performance drop,

performance may not be jk's focus...

" and they are pretty darn reliable.

five-nines?  some situations need that.

" Is your use case so critical that the faint chance of data loss is a killer,
" while the likely loss of performance is acceptable?  (then why do you have
" fusionio cards?)
" 
" Man that was worthless.  I suspect the customer has spent a lot of money on
" that third fusionio card, which will buy them next to nothing, but their
" approach will work fine for what it is.
" Nick
" 
" 
" On Thu, Nov 7, 2013 at 11:29 AM, Sandwich Maker <adh at an.bradford.ma.us>wrote:
" 
" > " From: Jonathan Katz <jon at jonworld.com>
" > "
" > " 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?
" >
" > what disksuite does in that situation is
" > a. mirror the drive pairs on each card
" > b. stripe the 6 mirrors
" > thus allowing you to survive any combination of 1-disk-per-card
" > failures.  it does this even if you try to configure 2 stripes and
" > mirror them, and it makes sense - with mirrored stripes, one failure
" > on each side would take you down.
" >
" > i would mirror first, then lvm the mirrors.  it would make sense to
" > mirror pairs across cards, to provide card-failure hardness.
________________________________________________________________________
Andrew Hay                                  the genius nature
internet rambler                            is to see what all have seen
adh at an.bradford.ma.us                       and think what none thought