From: Eric Sandeen <sandeen@redhat.com>
To: Phillip Susi <psusi@ubuntu.com>
Cc: Rabeeh Khoury <rabeeh3000@gmail.com>, linux-ext4@vger.kernel.org
Subject: Re: 16 TB filesystem limit on 32bit machine
Date: Mon, 20 Feb 2012 16:50:49 -0600 [thread overview]
Message-ID: <4F42CE49.80209@redhat.com> (raw)
In-Reply-To: <4F42B86B.60706@ubuntu.com>
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On 2/20/12 3:17 PM, Phillip Susi wrote:
> On 2/20/2012 11:50 AM, Eric Sandeen wrote:
>> fs metadata is mapped into an address space, IIRC, so can't be
>> addressed past 2^32 pages. Also, mkfs can't do buffered IO to the
>> device past 16T (it is writing to a device _file_) and ditto for
>> e2fsck.
>
> But the file is only used for open(), after that the IO is handled by
> the correct device driver, which handles 64 bit offsets ( when you
> have CONFIG_LBDAF on ). So if you can change the page cache index
> size ( and it doesn't blow up ) this should work fine.
Oh, sure - if you change pgoff_t to 64 bits, but until then, you
can't even mkfs.ext4 a device larger than 16T; there is nowhere
for that buffered IO to go in the page cache, right?
(You could mkfs.ext4 a 16T partition on a 40T lun today, thanks
to LBDAF, but not a 17T without changing pgoff_t et al)
And "if you change the page cache index size" that's a big leap
of faith, today. Might be interesting work to do, but I'd bet
it's a real chunk of work.
- -Eric
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prev parent reply other threads:[~2012-02-20 22:50 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-20 15:31 16 TB filesystem limit on 32bit machine Rabeeh Khoury
2012-02-20 16:50 ` Eric Sandeen
2012-02-20 21:17 ` Phillip Susi
2012-02-20 22:50 ` Eric Sandeen [this message]
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