bits vs bytes.... D'oh! again. It's a good job I don't do these calculations
professionally. :-)> Date: Tue, 15 Jul 2008 02:30:33 -0400> From: [EMAIL
PROTECTED]> To: [EMAIL PROTECTED]> Subject: Re: [zfs-discuss] please help with
raid / failure / rebuild calculations> CC: zfs-discuss@opensolaris.org> > 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.> > Will
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