Messages in this thread | | | Date | Wed, 29 Jun 2005 13:56:41 -0700 | From | Chris Wedgwood <> | Subject | Re: XFS corruption during power-blackout |
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On Wed, Jun 29, 2005 at 12:56:12PM -0500, Steve Lord wrote:
> There are also cool bits of technology which use the rotational > energy of the spinning down drive to dump the cache out to a special > track (or this may be an urban legend, not sure).
This seems only to be true for very small writes. I suspect on power loss a drive and finish writing the current sector.
Anyhow, I've tested power loss on drives with caching enabled and they definatley do lose data. Sometimes a couple of MBs worth.
I don't know if this is true for all drives but NONE of the ones I had access to when testing did anything like save the cache --- pretty much all data that was inflight got lost.
> I did spend a bunch of time once ensuring that when you typed sync > on xfs you could pull the power right after that and everything from > before the sync survived.
I think this is probably still true. If I sync then drop power I don't seem to have any problems provided caching is off.
If caching is enabled I still lose data. Linux does have a concept of write barriers but these are presently not implemented for XFS right now. Once they are I assume sunc + poweroff will be reliable with caching enabled. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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