Messages in this thread |  | | From | "Martin Eriksson" <> | Subject | Re: Journaling pointless with today's hard disks? | Date | Tue, 27 Nov 2001 18:42:00 +0100 |
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----- Original Message ----- From: "Matthias Andree" <matthias.andree@stud.uni-dortmund.de> To: <linux-kernel@vger.kernel.org> Sent: Tuesday, November 27, 2001 5:39 PM Subject: Re: Journaling pointless with today's hard disks?
<snip> > > Two things: > > 1- power loss. Fixing things to write to disk is bound to fail in > adverse conditions. If the drive suffers from write problems and the > write takes longer than the charge of your capacitor lasts, your > data is still toasted. nonvolatile memory with finite write time > (like NVRAM/Flash) will help to save the Cache. I don't think vendors > will do that soon. > > 2- error handling with good power: with automatic remapping turned on, > there's no problem, the drive can re-write a block it has taken > responsibility of, IBM DTLA drives will automatically switch off the > write cache when the number of spare block gets low. > > with automatic remapping turned off, write errors with enabled write > cache get a real problem because the way it is now, when the drive > reports the problem, the block has already expired from the write > queue and is no longer available to be rescheduled. That may mean > that although fsync() completed OK your block is gone.
I think we have gotten away from the original subject. The problem (as I understood it) wasn't that we don't have time to write the whole cache... the problem is that the hard disk stops in the middle of a write, not updating the CRC of the sector, thus making it report as a bad sector when trying to recover from the failure. No?
I think most people here are convinced that there is not time to write a several-MB (worst case) cache to the platters in case of a power failure. Special drives for this case could of course be manufactured, and here's for a theory of mine: Wouldn't a battery backed-up SRAM cache do the thing?
Anyway, maybe it is just me who have been thrown off-track? Are we discussing something else now maybe?
<snap>
_____________________________________________________ | Martin Eriksson <nitrax@giron.wox.org> | MSc CSE student, department of Computing Science | Umeå University, Sweden
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