🚀 go-pugleaf

Multiple issues going on here.  Malcolm's answer was accurate, Ron's was
either confused or confusing.

Don't muddle things by comparing arrays with the same number of disks:  you
need however much (non-parity) disk space you need, period, so compare
arrays with equal amounts of (non-parity) space.

In that case, RAID-5

1) is cheaper (n + 1 disks vs. 2n disks for RAID-1),

2) has single-threaded Read performance similar to RAID-1 (assuming RAID-1
uses striped mirroring when n > 1),

3) has multi-threaded Read performance inferior to RAID-1 (RAID-1 can
distribute the Reads over twice as many disks),

4) has significantly slower write performance than RAID-1 (unless you're
doing stripe-aligned full-stripe writes, in which case performance is about
equal),

5) is less robust than RAID-1 if two disks fail simultaneously (when n > 1,
two disk failures destroy RAID-1 data only if they hit a mirror pair), and

6) suffers more performance degradation during rebuild of a failed disk than
RAID-1 (the entire array is involved in the rebuild activity, not just one
disk).

RAID-1 also has the advantage of somewhat more flexible configurability -
e.g., if you concatenate (rather than stripe) the disk set, it may be easier
to expand it incrementally (given a file system that can deal with that),
and if you can find a controller that supports it you can choose to use a
'chained declustered' layout that lessens performance degradation during
replacement of a failed disk (though at the expense of the added robustness
described in -5- above).

Hope that helps,

- bill

Shaman <shaman@ihug.co.nz> wrote in message
news:37F548BD.AFB2D67@ihug.co.nz...
> Hi
>
> Anyway back to the topic (RAid 1 vs 5; write performance  and overall
> performance for a file and print server with a hardware RAID card.)
>
> I was aware of the need to calculate parity during the write in RAID 5 but
I
> thought the ability to write a small peice of the whole file to each disk
(in
> RAID 5) would be more significant timewise.
>
> Does RAID 5 ever get better than RAID 1,  as you add disks?
>
> ie RAID 1 vs   a  8  Disk RAID 5
> is RAID 1 still better?
>
> David
>
>
>
> Jim Pappe wrote:
>
> > with Raid 5 plus hot spare - 2 drive can fail ..
> > www.raidexpert.com
> >
> > Mark Landin <m555@earthlink.net> wrote in message
> > news:37e660eb.12904299@news.earthlink.net...
> > > On Fri, 17 Sep 1999 07:54:19 +0100, "Steven Perez"
> > > <steve@uninet.demon.co.uk> wrote:
> > >
> > > >Kenneth:
> > > >
> > > >Go with RAID 1/0  Stripe, and mirror. This will give the very best
> > > >performance, and availability, although it will give the least amount
of
> > > >storage.
> > >
> > > How is RAID 0/1 more "available" than RAID 5?
> > >
> > >
>