Date: Thu, 28 Oct 1999 18:55:53 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: "Chris D. Faulhaber" <cdf.lists@fxp.org>, Michael Beckmann <petzi@apfel.de>, hackers@FreeBSD.ORG Subject: Re: Limitations in FreeBSD Message-ID: <199910290155.SAA14208@apollo.backplane.com> References: <Pine.GSO.3.96.991028204307.27652C-100000@sol.cs.binghamton.edu>
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:>
:> The document is not quite right. The maximum size is limited to
:> 8 Terrabytes due to block-size conversions done in the kernel which are
:> independant of the filesystem block size.
:
:Can you tell me how to get the 8TB value? I know all the things about
:indirect blocks and I know that we use negative numbers for those indirect
:blocks. Thanks.
:
:-Zhihui
The kernel uses 512 byte blocks internally. 32 bit block number
quantities are used. To avoid sign problems we only allow 31 bits to
be used within the kernel (negative block number quantities are also
used within the kernel to identify meta-data).
So: 2^31 = 2 billion x 512 = 1 TB. Hmm. That isn't 8 TB.
I think we might have a problem over 1 TB with mmap() and the VM system.
Grr. Maybe the I/O subsystem too.
-Matt
Matthew Dillon
<dillon@backplane.com>
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