Re: EMC Drives

I've seen a problem with EMC drives some time ago .  I don't know whether it was
fixed by now.
When AS/400 writes journal entries to hard drive, it sends a write-through
command to disk subsystem, which means that it should not be put in cache and
should go directly to drive surface - this is needed to guarantee that journal
entries are safe.
EMC will still put data to their cache and signal completion to system. System
will think that journal data are on disk, while it is still in cache. Of course,
it is much faster, but if EMC subsystem will fail at this moment, journal data
will be lost.
This may adversely affect data recovery, because OS/400 recovery algorithms
assume that data is written to disk in a certain sequence.

Best regards
    Alexey Pytel



eric <eric@norcov.com> on 05/18/99 01:32:18 PM

Please respond to MIDRANGE-L@midrange.com

To:   "'midrange-l@midrange.com'" <midrange-l@midrange.com>
cc:    (bcc: Alexei Pytel/Rochester/IBM)
Subject:  EMC Drives





     My parent company is considering purchasing EMC drives for their new 7XX
AS/400.  They will be purchasing almost a terabyte of DASD.  Does anyone
have any thoughts as to why they should or shouldn't do this.  Thanks in
advance for any assistance.

Eric Kempter
CommAir Mechanical Services, Inc.


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