7c0e570888
The number of blocks that can be discarded in one BLKDISCARD ioctl on a zvol is currently unlimited. Some applications, such as mkfs, discard the whole volume at once and they use the maximum possible discard size to do that. As a result, several gigabytes discard requests are not uncommon. Unfortunately, if a large amount of data is allocated in the zvol, ZFS can be quite slow to process discard requests. This is especially true if the volblocksize is low (e.g. the 8K default). As a result, very large discard requests can take a very long time (seconds to minutes under heavy load) to complete. This can cause a number of problems, most notably if the zvol is accessed remotely (e.g. via iSCSI), in which case the client has a high probability of timing out on the request. This patch solves the issue by adding a new tunable module parameter: zvol_max_discard_blocks. This indicates the maximum possible range, in zvol blocks, of one discard operation. It is set by default to 16384 blocks, which appears to be a good tradeoff. Using the default volblocksize of 8K this is equivalent to 128 MB. When using the maximum volblocksize of 128K this is equivalent to 2 GB. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #858
Native ZFS for Linux! ZFS is an advanced file system and volume manager which was originally developed for Solaris. It has been successfully ported to FreeBSD and now there is a functional Linux ZFS kernel port too. The port currently includes a fully functional and stable SPA, DMU, and ZVOL with a ZFS Posix Layer (ZPL) on the way!
$ ./configure
$ make pkg
To copy the kernel code inside your kernel source tree for builtin compilation:
$ ./configure --enable-linux-builtin --with-linux=/usr/src/linux-...
$ ./copy-builtin /usr/src/linux-...
Full documentation for building, configuring, and using ZFS can be found at: http://zfsonlinux.org