Re: Raid 5 Vs Mirroring Performance

["Al Barsa, Jr." <barsa2@xxxxxxx>]

At 02:19 PM 2/3/98 -0600, you wrote:
>We use Raid 5 on all of our AS/400's.  Recently a Unix admin told me that
we would gain a lot of performance if we would mirror our disk drives
instead.  Does anyone know how much performance we are giving up by using
RAID 5 vs mirroring....

This is true.  You will also go from California to Florida much faster in a
jet liner than you will in a 25 yr old VW bug, however, there is a also
differential.  The following page comes from one of my COMMON pitches:

·  RAID-5 versus Mirroring: 
        The purpose of RAID-5 and mirroring is different 

· Additional protection 
        · Mirroring will protect controllers, IOPs and busses 
        · RAID-5 will not 

· Performance comparison - normal operations 
        · RAID-5  does 4 I/O per write 
        · Mirroring does 2 I/O per write 
        · Mirroring can read from either unit of the mirrored pair 

· Performance comparison - after failure 
        · RAID-5 suffers a performance degradation
        · Mirroring performance is normal 

· Additional DA$D required 
        · RAID-5 needs one extra per checksum set 
        · Mirroring needs twice as much 
 
Al

Al Barsa, Jr. - Account for Midrange-L
Barsa Consulting, LLC.  
400 > 390

Phone:  914-251-9400
Fax:    914-251-9406





Private mail should be sent to barsa@ibm.net
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