[Btrfs-devel] Handling of big volumes in btrfs

Jan Engelhardt jengelh at computergmbh.de
Sat Jan 19 14:22:03 PST 2008


>From the XFS list I gather that btrfs, being able to mount a >16 TB 
volume on a 32-bit x86 box, either has some special power - or bug.
Which of the two is it?

---------- Forwarded message ----------
Date: Sat, 19 Jan 2008 15:26:26 -0600
From: Eric Sandeen
Subject: Re: Volume too big

Jan Engelhardt wrote:
> On Jan 19 2008 14:41, Eric Sandeen wrote:

>> It's possible that btrfs can cope with this somehow - but also quite
>> possible that it's just missing the right checks :)
> I am not sure why Linux would be limited to 16 TB. If LBD is on,
> things are 64 bit, so I would expect to have at least access to
> 2 exabyte.

64-bit sector addressing, but there is a 32-bit index into the (4k)

2^32 * 4096 is 16T

So an address space has a 16T limit.

Even mkfs, if it needs to write past 16T (and I think mkfs.btrfs doesn't
need that...) will have trouble, if the device is > 16T - unless mkfs
uses direct IO.


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