Re: RAID1 3+ drives

[Roman Mamedov <rm@romanrm.net>]

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On Sat, 28 Jun 2014 04:26:43 +0000 (UTC)
Duncan <1i5t5.duncan@cox.net> wrote:

> Russell Coker posted on Sat, 28 Jun 2014 10:51:00 +1000 as excerpted:
> 
> > On Fri, 27 Jun 2014 20:30:32 Zack Coffey wrote:
> >> Can I get more protection by using more than 2 drives?
> >> 
> >> I had an onboard RAID a few years back that would let me use RAID1
> >> across up to 4 drives.
> >> 
> > Currently the only RAID level that fully works in BTRFS is RAID-1 with
> > data on 2 disks.
> 
> Not /quite/ correct.  Raid0 works, but of course that isn't exactly 
> "RAID" as it's not "redundant".  And raid10 works.  But that's simply 
> raid0 over raid1.  So depending on whether you consider raid0 actually 
> "RAID" or not, which in turn depends on how strict you are with the 
> "redundant" part, there is or is not more than btrfs raid1 working.

Also depending on what you consider "fully works", RAID1 may not qualify too,
as neither the read-balancing, nor write-submission algorithms are ready for
production use, performance-wise.

(RAID1 writes to two disks sequentially, not at the same time; and reads are
satisfied from in effect a random device, not from the least-busy device).

-- 
With respect,
Roman

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