RE: RAID question

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

At 11:03 AM 9/4/98 -0600, you wrote:

I respectfully disagree.  I originally purchased an S10 with 5 4 GB drives.
 The parity was equally spread over all 5 drives.  I then purchased another
5 4GB drives, and it set up another parity set!  (So I was now wasting two
full drives for redundancy.)  When I meekly and mildly expressed my
disappointment to Rochester (No, not the man that used to polish Mr.
Benny's car.) I was informed that if I added less than four drives at a
time, they would have been added to the same parity set, but four or more
went into their own parity set.  To recoup the lost space, I had to end
RAID and restart it.  The system then put the parity on the first eight
drives, so I only lost one for redundancy.

Al


>Err, with all due respect Al !  :-)
>
>Parity is spread over either 4 drives or 8.
>You saw the lower available disk capacity of 3145MB on the first 4
>drives.
>Then you add 2.  You haven't added 4 so the parity information is STILL
>only spread over the first 4 drives (your new drives show the full
>4194MB available).
>If you add another drive it will also show 4194MB available as parity is
>still spread over the first 4 drives.
>If you add an 8th drive you can now go into DST and RAID-5 will be
>spread over all 8 drives, so each will now show 3670MB.
>On many controllers you can add up to 10 drives.  So if you added an 8th
>or 9th drive the parity information stays spread over the dirst 8
>drives, and the 9th & 10th drive will show the full 4194MB available.
>
>
>Neil Palmer                                AS/400~~~~~      
>NxTrend Technology - Canada   ____________          ___  ~     
>Thornhill, Ontario,  Canada   |OOOOOOOOOO| ________  o|__||=   
>Phone: (905) 731-9000  x238   |__________|_|______|_|______)   
>Cell.: (416) 565-1682  x238    oo      oo   oo  oo   OOOo=o\   
>Fax:   (905) 731-9202       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
>mailto:NPalmer@NxTrend.com    AS/400  The Ultimate Business Server      
>http://www.NxTrend.com
>
>> -----Original Message-----
>> From:        Al Barsa, Jr. [SMTP:barsa2@ibm.net]
>> Sent:        Friday, September 04, 1998 11:10 AM
>> To:  MIDRANGE-L@midrange.com
>> Subject:     Re: RAID question
>> 
>> At 09:12 AM 9/4/98 -0500, you wrote:
>> >We just added 2 drives to an S20 that previously had 4 drives on it
>> (one
>> >RAID set).  I used SST to add the new drives to device parity
>> protection
>> >and then added them to my ASP.  As we were not adding a full RAID
>> set, I
>> >expected the system to mirror the devices.  Instead, I see this on
>> the
>> >WRKDSKSTS display:
>> >
>> >                    --Protection--            --Protected--
>> >Unit      ASP       Type      Status          Size
>> >1         1    DPY       ACTIVE          3145
>> >2         1    DPY       ACTIVE          3145
>> >3         1    DPY       ACTIVE          3145
>> >4         1    DPY       ACTIVE          3145
>> >5         1    DPY       ACTIVE          4194
>> >6         1    DPY       ACTIVE          4194
>> >
>> >This gives more DASD than if the new drives were irrored, but are
>> they
>> >really protected?  If so, why am I seeing all 4194 MB?
>> >We are at V4R1.
>> 
>> Good question.  In this case, the system only spread the parity over
>> the
>> base four drives.  If you turned RAID off and then back again on (in
>> which
>> case Murphy would have a disk failure at the exact moment of no
>> protection), parity would be spread over all six drives, up to a
>> maximum of
>> 8 on the disk controller on your system with just the base
>> controllers.
>> 
>> Al
>> 
>> 
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Al Barsa, Jr. - Account for Midrange-L
Barsa Consulting, LLC.  
400 > 390

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Fax:    914-251-9406


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