Date: Sat, 05 May 2001 09:31:09 -0700 From: Nick Sayer <nsayer@quack.kfu.com> To: Doug Russell <drussell@saturn-tech.com> Cc: stable <stable@FreeBSD.ORG> Subject: Re: soft update should be default Message-ID: <3AF42ACD.5000500@quack.kfu.com> References: <Pine.BSF.4.21.0105050657050.94973-100000@beastie.saturn-tech.com>
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Doug Russell wrote: > On Sat, 5 May 2001, Cy Schubert - ITSD Open Systems Group wrote: > > >> Of course as Gordon writes above, all bets are off if your disk does >> write-caching. > > > I still don't totally understand this. In the case of a drive with WCE, > aren't we always assuming that the drive will correctly write the data out > eventually, even if the system crashes? Yes. But that assumption is flawed. > > This assumes that we aren't talking about a power failure, here, but if it > is an external drive array with dual power supplies, at least one battery > backed, it doesn't matter even if the compuer power is cut, the drive > should still eventually flush out it's cache, shouldn't it? That may be the original intent, but cheap IDE drives let you turn on write caching, and they're for sure not battery-backed (nor do they attempt to store enough power at power-off to write back the cache with the remaining rotational latency or any such trickery). They lie about it. Write caching is evil unless you specifically know that it's being battery backed. 99.44% of the time, that's not the case. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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