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Only with a UPSOnly with a UPSPosted Sep 10, 2009 18:18 UTC (Thu) by aliguori (subscriber, #30636)In reply to: Only with a UPS by ncm Parent article: POSIX v. reality: A position on O_PONIES
<i>Second, more subtle but probably more important, drives lie about what is physically on disk.</i>
Not really. You can make a disk tell you when data is actually on the platter vs in the write cache. Furthermore, most "enterprise" drives have battery-backed write caches that guarantee enough power for the write caches to be flushed.
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Only with a UPS Posted Sep 10, 2009 19:06 UTC (Thu) by ncm (subscriber, #165) [Link] You can make a disk tell you when data is actually on the platterNo, you can ask a disk to tell you. It might even be honest about it if you never get the buffer too full. The commercial incentives to lie for the sake of benchmarks are extremely strong. Drives that don't lie cost a lot more, and are slower. Honesty is an extra-cost option. If you don't pay for honesty (few do) you won't get it. Honesty usually costs a lot more than a UPS.
Only with a UPS Posted Sep 10, 2009 19:12 UTC (Thu) by dlang (✭ supporter ✭, #313) [Link]
I have yet to see a drive that includes battery backup in it, and I work at a place that spends millions of dollars a year on enterprise grade storage
I think this is a myth like the drives that use platter energy to power themselves to write their buffer.
if you can point to a drive that includes a battery backup on the drive please post a link to it.
Only with a UPS Posted Sep 10, 2009 19:22 UTC (Thu) by ncm (subscriber, #165) [Link]
I suspect aliguori is referring to disk-array boxes, not drives.
Only with a UPS Posted Sep 11, 2009 16:24 UTC (Fri) by nix (subscriber, #2304) [Link]
Even then... it's just occurred to me that while I know my Areca RAID
controller has its own battery-backed cache, I have no idea whether it's asked the drives it controls to turn off *their* internal write cache... (Obviously we don't want that cache, as it's not battery-backed in any way.)
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