Date: Mon, 31 Mar 2008 14:34:29 -0700 From: "Martin Fouts" <mfouts@danger.com> To: "Matthew Dillon" <dillon@apollo.backplane.com> Cc: Christopher Arnold <chris@arnold.se>, arch@freebsd.org, qpadla@gmail.com, freebsd-arch@freebsd.org Subject: RE: Flash disks and FFS layout heuristics Message-ID: <B95CEC1093787C4DB3655EF330984818051D0A@EXCHANGE.danger.com> In-Reply-To: <200803312006.m2VK6Aom028133@apollo.backplane.com> References: <20080330231544.A96475@localhost> <200803310135.m2V1ZpiN018354@apollo.backplane.com> <B95CEC1093787C4DB3655EF330984818051D03@EXCHANGE.danger.com> <200803312125.29325.qpadla@gmail.com> <200803311915.m2VJFSoR027593@apollo.backplane.com> <B95CEC1093787C4DB3655EF330984818051D09@EXCHANGE.danger.com> <200803312006.m2VK6Aom028133@apollo.backplane.com>
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=20 > -----Original Message----- > From: Matthew Dillon [mailto:dillon@apollo.backplane.com]=20 > Sent: Monday, March 31, 2008 1:06 PM > To: Martin Fouts > Cc: qpadla@gmail.com; freebsd-arch@freebsd.org; Christopher=20 > Arnold; arch@freebsd.org > Subject: RE: Flash disks and FFS layout heuristics >=20 >=20 > But how do you index that information? You can't simply=20 > append the information to the NAND unless you also have a way to=20 > access it. So does the filesystem have to scan the NAND (or significant=20 > portions of it) in order to build an index of the filesystem topology in=20 > system memory? >=20 > No matter what you do you have to index the information=20 > *SOMEWHERE*. And NAND devices have a *SOMEWHERE* that makes them different than other persistent storage devices in ways that make them interesting to do file systems for. It's not _that_ you have to scan the NAND, by the way, it's _when_ you scan the NAND that has the major impact on performance.
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