From mboxrd@z Thu Jan 1 00:00:00 1970 From: jim owens Subject: Re: Converting system to raid Date: Sun, 12 Apr 2009 12:43:06 -0400 Message-ID: <49E21A1A.4020004@hp.com> References: <003801c9b96d$21a0f420$0a00a8c0@vorg> <49DF0D06.8030705@musmo.com> <20090410195303.GB21242@cthulhu.home.robinhill.me.uk> <00cc01c9ba1d$3aefecf0$0a00a8c0@vorg> <20090410205942.GC21242@cthulhu.home.robinhill.me.uk> <00f301c9ba23$032025f0$0a00a8c0@vorg> <20090410215129.GD21242@cthulhu.home.robinhill.me.uk> <019701c9ba66$aeed5630$0a00a8c0@vorg> <20090411143642.GA9915@cthulhu.home.robinhill.me.uk> <49E0B188.8050009@hp.com> <49E0BAF9.3090209@garzik.org> <49E0D60E.7040904@hp.com> <49E1CC6F.7020409@garzik.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49E1CC6F.7020409@garzik.org> Sender: linux-raid-owner@vger.kernel.org To: Jeff Garzik Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids To continue the pointless (but maybe entertaining) argument :) Jeff Garzik wrote: > jim owens wrote: >> The filesystem mod-time might have nanoseconds in it, but >> that does not mean 2 writes 100 nanoseconds apart will have >> different mod-times. > > Modern Linux filesystems absolutely do do metadata updates at that level > of granularity. In filesystems it only counts if it makes it to disk. 10,000,000 write-to-disk metadata updates per second? I think not. Even the top-of-the-line intel ssd can only do 3,300 writes per second. > Are you guaranteed district timestamps between writes? No, but then > again, metadata updates were never guaranteed between two writes either. > You might just be dirtying a mmap'd page, for example. So this sounds like you at least agree with my original statement that mod-time is not a 100% guarantee that no write occurred after you read a particular block of a file. Regardless of the fact we disagree about how accurate filesystems record times. jim