On May 7, 2009, at 4:50 PM, Tony Abernethy wrote: > >> > There are exotic ways of increasing risk by keeping the most of the > not-failed-yet neighbors as supposedly good sectors.
Not with a modern disk. The drives now essentially lie about where on the disk any given block is, you'll never know if block N is anywhere (physically) near block N-1 or N+1. Starting about 15 years ago, the most reasonable check I could find was the 'verify' command in solaris' 'format' command (which I've yet to find/write a simple alternative to). Anything else is just a waste of time. What this did was basically write a block of random bits, then read and compare. You need to do both, because some blocks are readable, but not writable, and vice versa. If you get a mismatch, the block was unreadable, and was (hopefully) remapped, so try again. The OS usually logs read and write errors (soft and/or hard) and you'd have some idea of the relative 'health' of the disk. Frankly, we would verify a disk if we hit a bad block, and if that remapped the bad block and produced no other errors over two passes, we'd keep using it (disks weren't that cheap then). If we got another error, we'd replace the disk. We got so many new disks that would encounter a bad block (and the OS would log the error) that we started verifying the disk when we got them to map out any bad blocks. . . Sean [demime 1.01d removed an attachment of type application/pkcs7-signature which had a name of smime.p7s]
