SUMMARY: Prestoserve and Disksuite Mirroring

From: James Ashton (jaa101@deakin.anu.edu.au)
Date: Tue May 11 1993 - 22:44:02 CDT


My original query asked about compatibility issues arising from using
Prestoserve with disk partitions mirrored with Online DiskSuite. Since
posting my question our local Sun technical people have told me that
this configuration is *not* supported since they can't guarantee that
the raw partitions are synchronised. They say maybe this will be fixed
in future releases :-(. My guess is that it will work most of the time
but that it could break just when you want mirroring to save you, i.e.
after a disk crash.

I'd also asked about performance issues and the possibility of prestoising
only one of the mirrored partitions. Mike Rafferty says:

>No, because both writes must complete before DiskSuite will return
>success on the write.

Christian Lawrence noted that:

>mirroring an fs carries almost no performance penalty (about ~5 % from what
>I can tell).
>
>think you *MUST* accelerate all drives in the mirror. for example, system
>panics, reboots, prestoserve flushes dirty buffers to the primary ONLY, then
>metadisk driver starts up and sandwiches itself between VFS and non-volatile
>devices. At this point, you do not have a mirror anymore and the state
>database does not reflect the inconsistency !! result: some time later all
>hell breaks loose and you're stuck restoring 10's of GB (yuk...double YUK).

I plan to move our vital files to a mirrored partition and turn off
prestoserve for that partition. For now we have to put up with the
performance hit to get the reliability. Prestoserve will remain in
effect for other (less vital) files so hopefully impact will be
minimal. Many thanks to the two respondants:

Christian Lawrence <cal@soac.bellcore.com.>
Mike Raffety <miker@il.us.swissbank.com.>

--
James Ashton						  System Administrator
VK2ZJA					     Department of Systems Engineering
Voice +61 6 249 0681	  Research School of Physical Sciences and Engineering
FAX   +61 6 249 2698				Australian National University
Email James.Ashton@anu.edu.au			   Canberra ACT 0200 Australia



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