Date: Fri, 15 Mar 2002 16:09:05 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Chris Mason <mason@suse.com> Cc: Josh MacDonald <jmacd@CS.Berkeley.EDU>, Parity Error <bootup@mail.ru>, freebsd-fs@FreeBSD.ORG, reiserfs-dev@namesys.com Subject: Re: [reiserfs-dev] Re: metadata update durability ordering/soft updates Message-ID: <3C928D21.404EA11D@mindspring.com> References: <E16lReK-000C3T-00@f10.mail.ru> <3C910C57.71C2D823@mindspring.com> <20020315065651.02637@helen.CS.Berkeley.EDU> <3C923C91.454D7710@mindspring.com> <1562810000.1016224776@tiny>
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Chris Mason wrote: > I haven't read the entire patent, but maybe you can point me to the > paragraphs where it covers write-ahead logging in the description. A subset of writes to secondary storage are performed using a Delayed Ordered Write (DOW) subsystem, which makes it possible for any file system to control the order in which modifications are propagated to disk. The DOW subsystem consists of two parts. The first part is a specification interface, which a file system implementation or any other kernel subsystem can use to indicate sequential ordering between a modification and some other modification of file system structural data. This is the write-ahead log. The only difference is where it's stored: in memory or on disk. The second part of DOW subsystem is a mechanism that ensures that the disk write operations are indeed performed in accordance with the order store. DOW improves computer system performance by reducing disk traffic as well as the number of context switches that would be generated if synchronous writes were used for ordering. See also claims 1, 6, 23, and 44. > Durning any operation, no attempt at all is made to order the writing > of the bitmap, the inode, the directory entries, or any other part of > the metadata. It simply makes sure that after a crash the operations > are either completed or not. If you mkdir foo and then mkdir foo2, > it is entirely possible the blocks for foo2 go to disk first. I didn't say it infringed Soft Updates (which does this), I said it infringed DOW (which doesn't). Soft Updates aren't infringible, in any case, since they are not patented. > The reiserfs log is also not a generic system module loosely coupled > from with the rest of the filesystem. The patent claims are generic enough that they could cover either case. Software patents are process patents, not performance patents. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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