On Tue, 2005-01-11 at 17:43, Guy wrote: > Good, your description is what I had assumed at first. But when I > re-read > the drive specs, it was vague, so I set ARRE back to 0. > > So, it should be a good thing to set it to 1, correct? I would. > Do you agree that Seagate's email is wrong? Or am I just reading it > wrong? I can't figure out what he is saying in the last sentence. I do believe that Seagate engineers are aware of the correct way to implement ARRE. I can't vouch for whether their firmware always gets it right. > I did not realize ARRE was a standard. I thought it was a Seagate > thing. > > Thanks, > Guy > > -----Original Message----- > From: linux-raid-owner@xxxxxxxxxxxxxxx > [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Tom Coughlan > Sent: Tuesday, January 11, 2005 9:35 AM > To: Guy > Cc: linux-raid@xxxxxxxxxxxxxxx > Subject: Re: hard disk re-locates bad block on read. > > On Mon, 2005-01-10 at 12:35, Guy wrote: > > My disks have the option to relocate bad blocks on read error. > > I was concerned that bogus data would be returned to the OS. > > > > They say CRC errors return corrupt data to the OS! I hope not! > > So it seems CRC errors and unreadable blocks both are corrupt or lost. > > But the OS does not know. > > So, I will leave this option turned off. > > > > Guy > > > > I sent this to Seagate: > > With ARRE (Automatic Read Reallocation Enable) turned on. Does it > relocate > > blocks that can't be read, or blocks that had correctable read problems? > > Or both? > > FWIW, the SCSI standard has been clear on this point for many years: > > "An ARRE bit of one indicates that the device server shall enable > automatic reallocation of defective data blocks during read operations. > ... The automatic reallocation shall then be performed only if the > device server successfully recovers the data. The recovered data shall > be placed in the reallocated block." (SBC-2) > > Blocks that can not be read are not relocated. The read command simply > returns an error to the OS. > > > > > If it re-locates un-readable blocks, then what data does it return to the > > OS? > > > > Thanks, > > Guy > > > > ================================================================== > > > > Guy, > > If the block is bad at a hardware level then it is reallocated and a > spare > > is used in it's place. In a bad block the data is lost, the sparing of the > > block is transparent to the operating system. Blocks with correctable read > > problems are one's with corrupt data at the OS level. > > > > Jimmie P. > > Seagate Technical Support > > - 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
