maarten <maarten@xxxxxxxxxxxx> wrote: > On Saturday 08 January 2005 19:55, you wrote: >> My disks claim to be able to re-locate bad blocks on read error. But I am >> not sure if this is correctable errors or not. If not correctable errors >> are re-located, what data does the drive return? Since I don't know, I ... > Afaik, if a drive senses it gets more 'difficult' than usual to read a sector, > it will automatically copy it to a spare sector and reassign it. However, I No, this is usually not the case. At least I don't know IDE drives that do so. This is why I call it `sector read error'. Each newer disk has some amount of `spare sectors' which can be used to relocate bad sectors. Usually, you have two situations where you can detect a bad sector: 1. If you write to it and this attempt fails and 2. If you read from it and this attempt fails. 1. would require some verify-operation, so I'm not sure if this is done at all in the wild. 2. has a simple problem: If you get a read-request for sector x and you cannot read it, what data should you return then? The answer is simple: you don't return data but an error (the read- error). Additionally you mark the sector as bad and relocate the next write-request for that sector to some spare sector and further read-requests then too. However, you still have to respond error messages for each subsequent read-request before the first relocated write-request appears. And afaik this is what current disks do. That's why you can just re-sync the failed disk to the array again without any problem - because the write-request happens then, the relocation takes place and everything's fine. regards, Mario -- The social dynamics of the net are a direct consequence of the fact that nobody has yet developed a Remote Strangulation Protocol. -- Larry Wall - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
