Re: wish for Linux MD mirrored raid types

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Roberto Spadim wrote:
hum, i asked this question one time, the point is:
raid1 code is very easy
raid10 code is more complex

easy = faster, less memory, less cpu
complex = faster?, more memory? more cpu?

check others raid system (freebsd, netbsd) and check how they do...

2011/5/6 Keld Jørn Simonsen<keld@xxxxxxxxxx>:
Keld Jørn Simonsen wrote:
As you say, RAID10,near on four disks is pretty much identical to
RAID1+0 - i.e., a stripe of two normal RAID1 pairs.


of course RAID10 offers the far option, and the option to run on an odd number of drives (I currently use it on a couple of 4-drive servers, but as I look at some replacement hardware I've been thinking that RAID10 on a 5-drive configuration offers a nice mix of reliability and performance)

re. easy/complex - I'm not sure I really believe that - when I've reviewed options, I come to the conclusion that:

RAID1 - wastes a lot of drive space, particularly if you want to maintain reliability after a single-drive failure (requires a minimum of 3 mirrored drives)

RAID5 and RAID6 are better when it comes to mixing efficiency with multi-drive failures, but have a couple of odd failure modes and are a real pain to rebuild after a failure

RAID1+0 and RAID0+1 are interesting combination - but my sense is that every time you nest a layer, you're adding configuration complexity, processing delays (low level cpu cycles and i/o transactions), and just that much more complexity if you have to reconfigure or rebuild and array (particularly if you're running LVM and DRBD on top of the basic disk arrays, as I am)

md RAID10 chops out a layer of nesting and makes better use of disk space - by combining block replication and striping into a single layer - providing what, to me, is a good balance of disk use, multiple copies of data, performance, and managability - so far, its worked well for me



--
In theory, there is no difference between theory and practice.
In<fnord>  practice, there is.   .... Yogi Berra


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