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    SubjectRe: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush
    On 2010-08-23 15:58, Ric Wheeler wrote:
    > On 08/23/2010 08:48 AM, Christoph Hellwig wrote:
    >> On Mon, Aug 23, 2010 at 02:30:33PM +0200, Tejun Heo wrote:
    >>> It might be useful to give several example configurations with
    >>> different cache configurations. I don't have much experience with
    >>> battery backed arrays but aren't they suppose to report write through
    >>> cache automatically?
    >> They usually do. I have one that doesn't, but SYNCHRONIZE CACHE on
    >> it is so fast that it effectively must be a no-op.
    > Arrays are not a problem in general - they normally have internally, redundant
    > batteries to hold up the cache.
    > The issue is when you have an internal hardware RAID card with a large cache.
    > Those cards sit in your server and the batteries on the card protect its
    > internal cache, but do not have the capacity to hold up the drives behind it.
    > Normally, those drives should have their write cache disabled, but sometimes
    > (especially with S-ATA disks) this is not done.

    The problem purely exists on arrays that report write back cache enabled
    AND don't implement SYNC_CACHE as a noop. Do any of them exist, or are
    they purely urban legend?

    Jens Axboe

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      Last update: 2010-08-23 16:03    [W:0.032 / U:82.640 seconds]
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