Richard Elling wrote:
On Mar 30, 2010, at 3:32 PM, Jeroen Roodhart wrote:
If you are going to trick the system into thinking a volatile cache is
nonvolatile, you
might as well disable the ZIL -- the data corruption potential is the same.
I'm sorry? I believe the F20 has a supercap or the like? The advise on:
You are correct, I misread the Marvell (as in F20) and X4540 (as in not X4500)
combination.
http://wikis.sun.com/display/Performance/Tuning+ZFS+for+the+F5100#TuningZFSfortheF5100-ZFSF5100
Is to disable write caching altogether. We opted not to do _that_ though... :)
Good idea. That recommendation is flawed for the general case and only
applies when all devices have nonvolatile caches.
Are you sure about disabling write cache on the F20 is a bad thing to do?
I agree that it is a reasonable choice.
For those following along at home, I'm pretty sure that the terminology
being used is confusing at best, and just plain wrong at worst.
The write cache is _not_ being disabled. The write cache is being marked
as non-volatile.
By marking the write cache as non-volatile, one is telling ZFS to not
issue cache flush commands.
BTW, why is a Sun/Oracle branded product not properly respecting the NV
bit in the cache flush command? This seems remarkably broken, and leads
to the amazingly bad advice given on the wiki referenced above.
--
Carson
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