Messages in this thread | | | Date | Mon, 10 Mar 2008 09:05:47 +1100 | From | David Chinner <> | Subject | Re: block layer / FS question: x86_32bit with LBD, 20 TB RAID volume => funny issues |
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On Thu, Mar 06, 2008 at 10:25:59PM +0100, Frantisek Rysanek wrote: > A few days ago, I've had my first opportunity to put my hands on a > 24bay RAID unit - configured for RAID 60, that's 20 TB of space in a > single chunk. I know that RAID units capable of this sort of capacity > have been on the market for some time now, so I was somewhat > surprised to discover that there are pending issues against Linux... > > The block device is detected/reported just fine. > I didn't even try Ext3, I know it's not appropriate for this sort of > capacity. I've tried Reiser3, and already mkfs.reiserfs (user-space > util) refused to create such a big FS. Then I tried XFS. The user- > space mkfs.xfs had no objections - so far so good. But when I tried > to mount the volume thus created, the kernel-space XFS driver > (including the one in 2.6.24.2) refused to mount the FS, complaining > about the FS being too big to be mounted on this platform.
Sure. the largest address space that can be used on a 32bit platform with 4k pages is 16TB (2^32 * 2^12 = 2^44 = 16TB). For XFS, that means metadata can't be placed higher in the filesystem than 16TB, and seeing as we only have a single address space for metadata, the filesystem is limited to 16TB. It could be fixed with software changes, but really there's no excuse for using x86 given how cheap x86_64 is now.....
> So far I've been using kernels compiled for 32bit mode x86. > Obviously I have LBD support enabled, and it's always worked > flawlessly. Would it be any help if I switched to 64bit mode? > My machines have been capable of that for a few years now, but so far > I had no reason to switch, as the memory capacities installed hardly > ever reached 4 GB...
Yes, switching to 64 bit machines will fix this problem as the address space will now hold 2^64*2^12 bytes.....
Cheers,
Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group
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