[wellylug] RAID5 with LVM

andrej at paradise.net.nz andrej at paradise.net.nz
Tue May 29 10:02:59 NZST 2007


Quoting Cliff Pratt <enkidu at cliffp.com>:

> > Honestly, RAID5 is a waste of resources. (And RAID4 and RAID3 ...)
> > Writes are slower than they need to be, and more importantly a data
> > error in your parity stripes will be unreported until it becomes
> > fatal, in most cases.
> That article is seriously funny! Might have been true a decade ago...
Heh ... and even that is debatable. :}

And the write-speed penalty dwindles away if you have more
than 6 spindles in  RAID-5, too ... I've done some excessive
testing in my last job where I was tasked to spec and set-up
an Oracle database server.  Went with an IBM SAN, and once I
hit the mark of 8 spindles in RAID-5 vs. RAID-10 the performance
differences in read-write speeds were negligible (may have to
do with the battery-buffered cache of the SAN, of course), with
reads being marginally faster on 5, and writes marginally faster 
on 10.  So really, it's a matter of what the application at hand
is.  If you're going to set-up a high-performance transactional
database system, by all means, go with 10 :} ... for any other
use (or specifically for file/app servers and data warehousing,
I'd go (and stick) with 5 because I get more SPACE for my bucks.

In the end, with the DBA jumping up and down and dragging in a 
contractor to back his view, the company went with 10 after all,
but I think they're wasting space ;}



> Cheers,
> 
> Cliff
Cheers,
Andrej




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