linux-kernel - Problems with large block devices in 64 bit kernels

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Date:	Thu, 07 Sep 2006 15:19:24 +0200
From:	Christian Schmid <webmaster@...idforum.com>
To:	linux-kernel@...r.kernel.org
Subject: Problems with large block devices in 64 bit kernels

Andries Brouwer wrote:

 > On Wed, Sep 06, 2006 at 10:54:42PM +0200, Christian Schmid wrote:
 >
 >> I run kernel 2.6.17.11 vanilla in 64 bit mode with 32 bit emulation.
 >> model name      : Intel(R) Xeon(R) CPU            5150  @ 2.66GHz
 >>
 >> Unfortunately there is no support for file-systems bigger than 2 TB in 64-bit mode with 32-bit 
emulation.
 >>
 >> erikm in #kernelnewbies told me to report it here:
 >>
 >> <Dragony> statfs("/MD2", 0xff8deca4)              = -1 EOVERFLOW (Value too large for defined 
data type)
 >
 >
 >
 > Hmm. statfs uses struct statfs which has a 4-byte f_blocks field,
 > and hence cannot hold larger values. You get what you ask for.
 >
 > statfs64 uses struct statfs64 which uses an 8-byte f_blocks field.
 >
 > (And then there is statvfs.)
 >
 > Andries


Hmm I dont think its that easy. Actually the max. value is 16 TB because of 232*4096 (block-size) 
and this works on a 32 bit kernel.

df on 32 bit kernel:
(See attached image. Sorry, this kernel has not the required network-driver included. Had to take a 
screenshot)

SAME df on 64 bit kernel:
write(1, "Filesystem           1K-blocks  "..., 67Filesystem           1K-blocks      Used Available 
Use% Mounted on
) = 67
statfs("/", {f_type=0x58465342, f_bsize=4096, f_blocks=732384, f_bfree=508015, f_files=2939776, 
f_ffree=2901955, f_namelen=255}) = 0
write(1, "/dev/md0               2929536  "..., 58/dev/md0               2929536    897476   2032060 
  31% /
) = 58
statfs("/proc", {f_type="PROC_SUPER_MAGIC", f_bsize=4096, f_blocks=0, f_bfree=0, f_files=0, 
f_ffree=0, f_namelen=255}) = 0
statfs("/MD1", {f_type=0x58465342, f_bsize=4096, f_blocks=4407104, f_bfree=4403156, 
f_files=17638656, f_ffree=17638645, f_namelen=255}) = 0
write(1, "/dev/md1              17628416  "..., 61/dev/md1              17628416     15792  17612624 
   1% /MD1
) = 61
statfs("/MD2", 0xffa30614)              = -1 EOVERFLOW (Value too large for defined data type)
write(2, "df: ", 4df: )                     = 4
write(2, "`/MD2\'", 6`/MD2')                  = 6
write(2, ": Value too large for defined da"..., 39: Value too large for defined data type) = 39
write(2, "\n", 1
)                       = 1
statfs("/dev/pts", {f_type=0x1cd1, f_bsize=4096, f_blocks=0, f_bfree=0, f_files=0, f_ffree=0, 
f_namelen=255}) = 0
munmap(0xf7eea000, 4096)                = 0

So its definetly something with the kernel.

Regards,
Christian Schmid

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