Re: With 4 disks should I go for RAID 5 or RAID 10 - Mailing list pgsql-performance

From Mark Mielke
Subject Re: With 4 disks should I go for RAID 5 or RAID 10
Date
Msg-id 4773C3AE.1060602@mark.mielke.cc
Whole thread Raw
In response to Re: With 4 disks should I go for RAID 5 or RAID 10  (Bill Moran <wmoran@collaborativefusion.com>)
Responses Re: With 4 disks should I go for RAID 5 or RAID 10
List pgsql-performance
Bill Moran wrote:
In response to Mark Mielke <mark@mark.mielke.cc>:
 
Bill Moran wrote:   
I'm fairly sure that FreeBSD's GEOM does.  Of course, it couldn't be doing
consistency checking at that point.     
According to this:

http://www.freebsd.org/cgi/man.cgi?query=gmirror&apropos=0&sektion=8&manpath=FreeBSD+6-current&format=html

There is a -b (balance) option that seems pretty clear that it does not 
read from all drives if it does not have to:   
>From where did you draw that conclusion?  Note that the "split" algorithm
(which is the default) divides requests up among multiple drives.  I'm
unclear as to how you reached a conclusion opposite of what the man page
says -- did you test and find it not to work? 
Perhaps you and I are speaking slightly different languages? :-) When I say "does not read from all drives", I mean "it will happily read from any of the drives to satisfy the request, and allows some level of configuration as to which drive it will select. It does not need to read all of the drives to satisfy the request."

Cheers,
mark

-- 
Mark Mielke <mark@mielke.cc>

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