On Wed, Apr 15, 2009 at 02:56:15PM -0500, Eric Sandeen wrote: > Valerie Aurora Henson wrote: > > On Wed, Apr 08, 2009 at 05:45:47PM -0400, Nick Dokos wrote: > > > >> but there is an interesting catch-22: how do I save its output? > >> > >> I can try the command line suggested in the manual page: > >> > >> e2image -r <dev> - | bzip2 > image.bz2 > >> > >> but it takes forever: I started a run on Saturday and it was not > >> done by Tuesday when I killed it - writing to the pipe at 4096 bytes > >> a pop is very slow. > >> > >> Or I can forego the compression and try to save to a file: it's sparse > >> (I only used 7GiB before it failed), but its nominal size exceeded the > >> maximum file size limit on ext4, at which point I start getting lseek > >> failures. > > We really need some e2image format which encodes the sparseness, I think... That seems like a low priority to me. But it would make a great Google Summer of Code project... > > The 16TB limit on ext4 files is an enormous pain for testing 64-bit > > (>= 16TB) file systems. I keep intending to write some simple dm > > setup to concatenate two loopback files together, but instead I always > > install XFS and create a loopback file on an XFS partition. > > For testing a large device, say /dev/sdb1 is 10GB large: > > # TERABYTES=`expr 20 \* 1024 \* 1024 \* 1024 \* 2` # 20 TB in sectors > # echo "0 $ERABYTES zero" | dmsetup create zero1 > # echo "0 $TERABYTES snapshot /dev/mapper/zero1 /dev/sdb1 p 128" | \ > dmsetup create sparse1 > > This will create a 20TB sparse device called /dev/mapper/sparse1 that > has 10GB of actual storage space available. If more than 10GB of data is > written to this device, it will start returning I/O errors. > > This is from Documentation/device-mapper/zero.txt Wow, that just rolls right off the tongue... Thanks for the pointer. I'm going to see if I can come up with something that I can memorize (although generally not hurting for a copy of the kernel source). -VAL -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
