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? Do you agree that Seagate's email is wrong? Or am I just reading it wrong? 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 - 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 - 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
