Will Murnane wrote: > On Tue, Jul 15, 2008 at 01:58, Ross <[EMAIL PROTECTED]> wrote: > >> However, I'm not sure where the 8 is coming from in your calculations. >> > Bits per byte ;) > > >> In this case approximately 13/100 or around 1 in 8 odds. >> > Taking into account the factor 8, and it's around 8 in 8. > > Another possible factor to consider in calculations of this nature is > that you probably won't get a single bit flipped here or there. If > drives take 512-byte sectors and apply Hamming codes to those 512 > bytes to get, say, 548 bytes of coded data that are actually written > to disk, you need to flip (548-512)/2=16 bytes = 128 bits before you > cannot correct them from the data you have. Thus, rather than getting > one incorrect bit in a particular 4096-bit sector, you're likely to > get all good sectors and one that's complete garbage. Unless the > manufacturers' specifications account for this, I would say the sector > error rate of the drive is about 1 in 4*(10**17). I have no idea > whether they account for this or not, but it'd be interesting (and > fairly doable) to test. Write a 1TB disk full of known data, then > read it and verify. Then repeat until you have seen incorrect sectors > a few times for a decent sample size, and store elsewhere what the > sector was supposed to be and what it actually was. >
The specification is for unrecoverable reads per bits read. I think most people expect this to be as delivered to host, which is how we count them. I would expect many, many more recoverable read events. You can also adjust by the amount of space used in ZFS and the number of copies of the data. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
