On Tue, 30 Jun 2009, Monish Shah wrote:
The evil tuning guide says "The ZIL is an essential part of ZFS and should
never be disabled." However, if you have a UPS, what can go wrong that
really requires ZIL?
Without addressing a single ZFS-specific issue:
* panics
* crashes
* hardware failures
- dead RAM
- dead CPU
- dead systemboard
- dead something else
* natural disasters
* UPS failure
* UPS failure (must be said twice)
* Human error (what does this button do?)
* Cabling problems (say, where did my disks go?)
* Malicious actions (Fired? Let me turn their power off!)
That's just a warm-up; I'm sure people can add both the ZFS-specific
reasons and also the fallacy that a UPS does anything more than mitigate
one particular single point of failure.
Don't forget to buy two UPSes and split your machine across both. And
don't forget to actually maintain the UPS. And check the batteries. And
schedule a load test.
The single best way to learn about the joys of UPS behaviour is to sit
down and have a drink with a facilities manager who has been doing the job
for at least ten years. At least you'll hear some funny stories about the
day a loose screw on one floor took out a house UPS and 100+ hosts and NEs
with it.
Andre.
--
Andre van Eyssen.
mail: an...@purplecow.org jabber: an...@interact.purplecow.org
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