Tom Lane <[EMAIL PROTECTED]> writes: > Greg Stark <[EMAIL PROTECTED]> writes: > > I'm a bit surprised that the write-cache lead to a corrupt database, and not > > merely lost transactions. I had the impression that drives still handled the > > writes in the order received. > > There'd be little point in having a cache if they did, I should think. > I thought the point of the cache was to allow the disk to schedule I/O > in an order that minimizes seek time (ie, such a disk has got its own > elevator queue or similar).
If that were the case then SCSI drives that ship with write caching disabled and using tagged command queuing instead would perform poorly. I think the main motivation for write caching on IDE drives is that the IDE protocol forces commands to be issued synchronously. So you can't send a second command until the first command has completed. Without write caching that limits the write bandwidth tremendously. Write caching is being used here as a poor man's tcq. -- greg ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
