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<div class="moz-cite-prefix">On 16/07/2015 19:38, Richard Elling
wrote:<br>
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<div class="">On Jul 16, 2015, at 11:30 AM, Schweiss, Chip
<<a moz-do-not-send="true"
href="mailto:chip@innovates.com" class="">chip@innovates.com</a>>
wrote:</div>
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<div class="">The 850 Pro should never be used as a
log device. It does not have power fail protection
of its ram cache. You might as well set
sync=disabled and skip using a log device entirely
because the 850 Pro is not protecting your last
transactions in case of power failure.<br class="">
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<div>Chip, are you asserting that the 850 Pro does not honor the
cache flush command?</div>
<div>In the bad old days, there were SSDs that were broken for
cache flushes, but some of</div>
<div>the most important (to Samsung) OSes, like Windows, rely on
cache flushes to work.</div>
<div>ZFS does as well.</div>
<div> -- richard</div>
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<br>
Was just in the middle of writing something similar when your reply
came in.<br>
Just to add, ZIL devices don't have to have power fail emergency
supply to work correctly.<br>
What's important is that they don't lie about when they get data to
non-volatile storage.<br>
Those with power fail protection can in many cases reply when data
hits their DRAM cache, whereas those without have to wait a bit
longer until the data hits the flash chips. So the difference tends
to impact latency of synchronous operations, but in both cases they
are very much faster than waiting until the data hits the platters
of spinning rust.<br>
<br>
-- <br>
Andrew Gabriel<br>
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