Messages in this thread | | | Date | Sat, 14 Jul 2001 23:05:36 -0700 (PDT) | From | John Alvord <> | Subject | Re: [PATCH] 64 bit scsi read/write |
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On Sun, 15 Jul 2001, Chris Wedgwood wrote:
> On Sat, Jul 14, 2001 at 10:11:30PM +0200, Daniel Phillips wrote: > > Atomic commit. The superblock, which references the updated > version of the filesystem, carries a sequence number and a > checksum. It is written to one of two alternating locations. On > restart, both locations are read and the highest numbered > superblock with a correct checksum is chosen as the new filesystem > root. > > Yes... and which ever part of the superblock contains the sequence > number must be written atomically. > > The point is, you _NEED_ to be sure that data written before the > superblock (or indeed anywhere further up the tree, you can make > changes in theory which don't require super-block updates) are written > firmly to the platters before any thing which refers to it is updated. > > Alan was saying with IDE you cannot reliably do this, I assume you can > with SCSI was my point.
In the IBM solution to this (1977-78, VM/CMS) the critical data was written at the begining and the end of the block. If the two data items didn't match then the block was rejected.
john alvord > > > > --cw > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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