David,

If you read thru my note, I wasn't engaged in any 'scare tactics'  but
was replying to the question 'if you were going to use AIX or ADSM
mirroring', which would you use. I was simply offering an opinion on
what I would use if those were my options  In my case, the ADSM DB is on
a 7137 disk array and this provides sufficient redundancy in the
hardware to warant not having to mirror the database.  However, when we
ran on ADSM on MVS, I made the decision to mirror the ADSM DB -  it was
spread out across many 3390-2 disks.  For those of you familiar with
mainframe disk technology, the 3390-2 disk drives had some reliability
problems as they became 'more mature' :-).  This saved me from having to
recover the ADSM DB on 5 different occasions over a 2-3 year period.
Any decision on mirroring or any form of redundancy needs to be
predicated by such things as how critical the system is, how long would
it take to recover, how much would it cost to provide that redundancy,
etc.

Tim

p.s. Doesn't DB2 provide other means of redundancy such as dual disk
logging, table mirroring, and MVS related stuff such as data set level
dual copy using SMS, etc. ?

>-----Original Message-----
>From:  Sanders, David [SMTP:DSanders AT INTERNAL.MASSMUTUAL DOT COM]
>Sent:  Tuesday, January 06, 1998 9:18 AM
>To:    ADSM-L AT VM.MARIST DOT EDU
>Subject:       Re: ADSM mirroring vs. AIX mirroring
>
>Wow, this sounds suspiciously like the old scare tactics that would
>cause folks to buy a ton of hardware!!  To double your capacity just so
>that you "have a prayer that a bad write during ADSM crashed" only got
>propogated to 1 of the mirrored sets, is unjustified.  Since ADSM is
>stable program-wise, if that improbable corruption occurred, how about
>using the recovery procedures?  MassMutual hasn't had ANY corruption of
>DB's (crossed fingers) in the last 2 years.  Think of how much mainframe
>DASD we've saved.  If this philosiphy was common practise,, would we
>have to mirror DB2 and other DB's??  Yikes, there goes the hardware
>budget!!!!!!!
>
>> -----Original Message-----
>> From: Pittson, Timothy ,HiServ/NA [SMTP:tpittson AT HIMAIL.HCC DOT COM]
>> Sent: Monday, January 05, 1998 11:45 AM
>> To:   ADSM-L AT VM.MARIST DOT EDU
>> Subject:      Re: ADSM mirroring vs. AIX mirroring
>>
>> Joe,
>>         If it comes down to using ADSM or AIX to mirror the database,
>> I'd use
>> ADSM mirroring.  I think the big advantage to using ADSM mirroring is
>> in
>> the event of the system crashing during a DB write and causing DB
>> corruption.  With AIX mirroring, I think you're SOL but with ADSM
>> mirroring, if the write didn't complete to both copies of the DB, you
>> stand a chance of one copy of the database not being corrupted.
>> Regarding RAID, I had posted questions to the ADSM-L listserver a
>> couple
>> of years ago about this and received some very helpful information -
>> somebody had even done some benchmarking (7137 array vs. SCSI vs. SSA
>> or
>> something like that - this was a long time ago - at the time, the 7137
>> outperformed the other options ).  We decided on using a dedicated
>> 7137-514 disk array configured for RAID-5 w/hot spare for our ADSM DB
>> (16 GB) and have been very happy with the performance.  There had also
>> been some posts about using mirroring/striping with SSA disks but I
>> don't know what the results of that were.  I keep the recovery logs on
>> separate dedicated SSA disks and use ADSM mirroring to mirror them.
>>
>> Tim Pittson
>>
>>
>> >-----Original Message-----
>> >From:  Joe Morris [SMTP:morris AT UNC DOT EDU]
>> >Sent:  Monday, January 05, 1998 10:49 AM
>> >To:    ADSM-L AT VM.MARIST DOT EDU
>> >Subject:       ADSM mirroring vs. AIX mirroring
>> >
>> >I've been browsing through the ADSM archives at Marist and could not
>> find
>> >what I was looking for.  Setting up a new server that has ample space
>> to
>> >replace our old ADSM server.
>> >
>> >What are the pros and cons of using ADSM and AIX to mirror the
>> database
>> >and log volumes.  Mainly focusing on differences between using AIX
>> >mirroring and the built-in mirroring in ADSM.
>> >
>> >I had considered a RAID configuration, but it seems like that is not
>> such
>> >a hot solution for the database for performance reasons.  Am I wrong?
>> >
>> >_______________________________________________________________
>> >Joe Morris  -  morris AT unc DOT edu  -  http://sunsite.unc.edu/morris
>> >Academic Technology and Networks, Development and Eval Services
>> >University of North Carolina at Chapel Hill      PGP by request