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    SubjectRe: wishful thinking about atomic, multi-sector or full MD stripe width, writes in storage
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    Ric Wheeler <rwheeler@redhat.com> writes:

    > The whole thread above is about software MD using commodity drives
    > (S-ATA or SAS) without battery backed write cache.

    Yes. However, you mentioned external RAID arrays disable disk caches.
    That's why I asked if they are using SATA or SCSI/etc. disks, and if
    they have battery-backed cache.

    > Also, when you enable the write cache (MD or not) you are buffering
    > multiple MB's of data that can go away on power loss. Far greater
    > (10x) the exposure that the partial RAID rewrite case worries about.

    The cache is flushed with working barriers. I guess it should be
    superior to disabled WB cache, in both performance and expected disk
    lifetime.
    --
    Krzysztof Halasa


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