Maximum block dev size / filesystem size

Maximum block dev size / filesystem size

[Aaron Peterson]

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I work for a company with a 15 TB SAN.  All opinions about the
disadvantages of creating really large filesystems aside, I'm trying to
find out what is the maximum filesystem size we can allocate on our SAN
that a linux box (x86) can really use.

I seem to be finding (from various posts on newsgroups and the kernel
source itself) that block devices with 2.4 kernels cannot exceed 2 TB,
so no matter what the filesystem can theoretically handle, 2 TB is the
practical limit.

I've read that XFS filesystems can theoretically be created up to 18
million TB in size.

What I can't seem to find anywhere is whether the 2 TB block device
limit has improved/grown with 2.6 kernels (on x86 hardware).  Perhaps
I've looked in the wrong places, but I haven't found anything.

If you have any helpful information, or can point me towards a better
place to look I would be very appreciative.

I am not joined to this list, so if you can CC: me in the reply I would
also be grateful.

Aaron

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Re: Maximum block dev size / filesystem size

[Alan Cox]

On Iau, 2004-10-07 at 21:19, Aaron Peterson wrote:
> I work for a company with a 15 TB SAN.  All opinions about the
> disadvantages of creating really large filesystems aside, I'm trying to
> find out what is the maximum filesystem size we can allocate on our SAN
> that a linux box (x86) can really use.

For 2.4.x 1Tb (2Tb works for some devices but its a bit variable)

> What I can't seem to find anywhere is whether the 2 TB block device
> limit has improved/grown with 2.6 kernels (on x86 hardware).  Perhaps
> I've looked in the wrong places, but I haven't found anything.

2.6 fixed this problem although it appears not for some specialist
cases. Last time I checked LVM logical volumes over 2Tb were reported
problematic.

Re: Maximum block dev size / filesystem size

[Aaron Peterson]

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On Thu, 2004-10-07 at 15:39, Alan Cox wrote:
> On Iau, 2004-10-07 at 21:19, Aaron Peterson wrote:
> > I work for a company with a 15 TB SAN.  All opinions about the
> > disadvantages of creating really large filesystems aside, I'm trying to
> > find out what is the maximum filesystem size we can allocate on our SAN
> > that a linux box (x86) can really use.
> 
> For 2.4.x 1Tb (2Tb works for some devices but its a bit variable)
> 
> > What I can't seem to find anywhere is whether the 2 TB block device
> > limit has improved/grown with 2.6 kernels (on x86 hardware).  Perhaps
> > I've looked in the wrong places, but I haven't found anything.
> 
> 2.6 fixed this problem although it appears not for some specialist
> cases. Last time I checked LVM logical volumes over 2Tb were reported
> problematic.

I've read that the other main difficulty besides block device size
limits is problems with the ext2 management tools themselves.  So, how
would you rate my chances of using a 2.6 kernel with XFS (and xfs
management tools of course) with a 5 TB filesystem?  Probably not a well
tested scenerio to say the least...

Aaron

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Re: Maximum block dev size / filesystem size

[Nathan Scott]

On Fri, Oct 08, 2004 at 10:13:53AM -0400, Aaron Peterson wrote:
> On Thu, 2004-10-07 at 15:39, Alan Cox wrote:
> > On Iau, 2004-10-07 at 21:19, Aaron Peterson wrote:
> > > I work for a company with a 15 TB SAN.  All opinions about the
> > > disadvantages of creating really large filesystems aside, I'm trying to
> > > find out what is the maximum filesystem size we can allocate on our SAN
> > > that a linux box (x86) can really use.
> > 
> > For 2.4.x 1Tb (2Tb works for some devices but its a bit variable)
> > 
> > > What I can't seem to find anywhere is whether the 2 TB block device
> > > limit has improved/grown with 2.6 kernels (on x86 hardware).  Perhaps
> > > I've looked in the wrong places, but I haven't found anything.
> > 
> > 2.6 fixed this problem although it appears not for some specialist
> > cases. Last time I checked LVM logical volumes over 2Tb were reported
> > problematic.
> 
> I've read that the other main difficulty besides block device size
> limits is problems with the ext2 management tools themselves.  So, how
> would you rate my chances of using a 2.6 kernel with XFS (and xfs
> management tools of course) with a 5 TB filesystem?  Probably not a well
> tested scenerio to say the least...

Assuming the device driver(s) you pick are happy with 64 bit sector
numbers, you should expect this to work (iow, you should not have
any trouble from XFS itself).  SGI ships 2.4 product with specific
supported drivers and the LBD patch (both 32 and 64 bit boxen) in
order to use large devices.

cheers.

-- 
Nathan