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Conference ssag::ask_ssag

Title:	Ask the Storage Architecture Group
Notice:	Check out our web page at http://www-starch.shr.dec.com
Moderator:	SSAG::TERZAN

Created:	Wed Oct 15 1986
Last Modified:	Fri Jun 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	6756
Total number of notes:	25276

6374.0. "Dual HSD30's with writeback cache, battery fail query" by POMPY::LESLIE (Andy, DEC man walking...) Wed Feb 05 1997 05:30

    I have 2 pairs of dual-redundant HSD30's with write-back cache enabled.
    
    I have been told that you cannot have write-back cache on only one of a
    redundant pair. What happens if the batteries fail on one HSD30?  Can
    you leave the write-back cache enabled on just one?
    
    Thanks
    
    Andy Leslie

T.R	Title	User	Personal Name	Date	Lines
6374.1		SSDEVO::KOWALL	StorageWorks Engineering Support	`Wed Feb 05 1997 10:36`	21
	-< Dual HSD30's with write-back cache, battery fail query >- Yes, if the drives must failover to continue running, (sets) you will still have write back as long as one cache module has good batteries. The drives that stay on the controller with the bad cache batteries will do write-through. Please read 5.1 in the Service Manual to fully understand low battery consideration with the different cache policies. JK I have 2 pairs of dual-redundant HSD30's with write-back cache enabled. I have been told that you cannot have write-back cache on only one of a redundant pair. What happens if the batteries fail on one HSD30? Can you leave the write-back cache enabled on just one? Thanks Andy Leslie
6374.2		SSDEVO::THOMPSON	Paul Thompson, Colorado Springs	`Wed Mar 26 1997 15:07`	5
	Just a clarification to -.1. When the batteries fail and the controller defaults to write-through mode, access to RAID and Mirror sets is denied because functional write back cache is a requirement to addres the "hole" issue in RAID and mirroring.