From owner-freebsd-hackers@FreeBSD.ORG  Thu Sep 16 17:59:43 2004
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Date: Thu, 16 Sep 2004 14:11:08 -0400
From: Gary Corcoran <garycor@comcast.net>
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To: Sam <sah@softcardsystems.com>
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Subject: Re: ZFS
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Sam wrote:

> On Thu, 16 Sep 2004, Jan Grant wrote:
> 
>> On Thu, 16 Sep 2004, Sam wrote:
>>
>>> Let's suppose you generate an exabyte of storage per year.  Filling a 
>>> 64-bit
>>> filesystem would take you approximately 8 million years.
>>
>>
>> Hang on, I'm not sure I know where these numbers are coming from.
>>
>> 1PB is - what? 2^50 bytes? That looks closer to 2^64 than your
>> figures indicate. I'd imagine an exabyte a year ought to be topping out
>> after 16 years. I'm missing about half-a-dozen orders of magnitude
>> somewhere it seems.
> 
> 
> 1PB is indeed 2^50 bytes, but filesystems don't address on the byte,
> but on the block (1K, 4K, 8k, ...).  The numbers I'm using assume
> the filesystem addresses on the sector, which is unrealistically
> small.  Jack it up to a 16K blocksize and you jump a few hundred
> ZB in size.

You have to be able to *seek* on a byte boundary.  Hence doesn't a
"64-bit" filesystem indeed mean "only" 2^64 bytes?

Gary