Thanks to all who responded to my question. Particularly thanks to:
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alan_at_nabeth.cxo.dec.com
janderson_at_NOVALIS.COM
francini_at_nashua.progress.com
labelles_at_mscd.edu
webster_at_ssdpdc.lgb.cal.boeing.com
mackey_at_pisello.wustl.edu
justin.richardson_at_redmar.com
silvestre_at_hotmail.com
emil_at_mobtel.co.yu
i769646_at_smrs013a.mdc.com
viktor.holmberg_at_abnamro.co.uk
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My question was:
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I am using HSZ40's in a dual-redundant configuration. When I do a SHOW THIS
FULL it reports "cache is good" and "battery is good" When I do a SHOW OTHER
FULL it reports "cache is good" and "battery is low." I also get a message
saying "cache battery charge is low" and "write-back caching is disabled." I
have writeback caching set for all units in this array.
Does the HSZ40 disable writeback caching automatically if the cache battery
is low, and does this override the writeback cache setting at the disk unit
level? In other words, is the hardware smart enough to protect me when the
cache battery fails?
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The overwhelming response was:
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Yes, if the battery is bad, settings or not, caching will be disabled.
Yes, I believe that modern versions of the firmware will turn off writeback
caching when the battery isn't in a desirable state. Older firmware versions
weren't very smart about handling the battery.
Yes, you can get the HSZ to serve if the batteries are LOW, but if the
batteries are in FAIL state it won't even let you have any access. You're
not seeing that because you've got dual-redundant controllers.
Yes, if the battery is low caching is disabled.
I had a similar probelm with a HSZ40 with a bad battery. Found that it
disabled write-back cacheing when the battery is low.
By disabling the cache when the battery condition is low the controller
automatically avoids any data loss if controller fails.
You're right, the hardware is smart enough to prevent you from data loss.
With battery low or fail, write back cache is disabled on that unit. The
only thing you should have in mind is to replace both batteries as soon as
possible and even the batteries that are good because if they were installed
at the same time of the others, they won't take so long.
There is one parameter on HSZ which determines behaviour in "battery bad"
situation. That parameter is CACHE_POLICY. Depending on value of this
parameter, HSZ can act two ways. If CACHE_POLICY is set to A, when batter is
bad HSZ sets all devices to offline to prevent accessing devices from hosts,
and to protect data. If CACHE_POLICY is set to B, when battery is bad HSZ
sets cache write method to write-through to protect system against data
loss.
Yep! Them HSZ40's is smart critters.
Yes, disabling write back cache is one of the features if the battery is
low.
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Again thanks, and thanks for making this list possible.
/Jim
Received on Fri Mar 26 1999 - 20:49:05 NZST