effectively caps the file size at `real_size - offset`. Can be combined with
:option:`size` to constrain the start and end range of the I/O workload.
A percentage can be specified by a number between 1 and 100 followed by '%',
- for example, ``offset=20%`` to specify 20%. In ZBD mode, value can be set as
+ for example, ``offset=20%`` to specify 20%. In ZBD mode, value can be set as
number of zones using 'z'.
.. option:: offset_align=int
If this option is not specified, fio will use the full size of the given
files or devices. If the files do not exist, size must be given. It is also
possible to give size as a percentage between 1 and 100. If ``size=20%`` is
- given, fio will use 20% of the full size of the given files or devices.
+ given, fio will use 20% of the full size of the given files or devices.
In ZBD mode, value can also be set as number of zones using 'z'.
Can be combined with :option:`offset` to constrain the start and end range
that I/O will be done within.
Select the xnvme async command interface. This can take these values.
**emu**
- This is default and used to emulate asynchronous I/O.
+ This is default and use to emulate asynchronous I/O by using a
+ single thread to create a queue pair on top of a synchronous
+ I/O interface using the NVMe driver IOCTL.
**thrpool**
- Use thread pool for Asynchronous I/O.
+ Emulate an asynchronous I/O interface with a pool of userspace
+ threads on top of a synchronous I/O interface using the NVMe
+ driver IOCTL. By default four threads are used.
**io_uring**
- Use Linux io_uring/liburing for Asynchronous I/O.
+ Linux native asynchronous I/O interface which supports both
+ direct and buffered I/O.
+ **io_uring_cmd**
+ Fast Linux native asynchronous I/O interface for NVMe pass
+ through commands. This only works with NVMe character device
+ (/dev/ngXnY).
**libaio**
Use Linux aio for Asynchronous I/O.
**posix**
- Use POSIX aio for Asynchronous I/O.
+ Use the posix asynchronous I/O interface to perform one or
+ more I/O operations asynchronously.
**nil**
- Use nil-io; For introspective perf. evaluation
+ Do not transfer any data; just pretend to. This is mainly used
+ for introspective performance evaluation.
.. option:: xnvme_sync=str : [xnvme]
Select the xnvme synchronous command interface. This can take these values.
**nvme**
- This is default and uses Linux NVMe Driver ioctl() for synchronous I/O.
+ This is default and uses Linux NVMe Driver ioctl() for
+ synchronous I/O.
**psync**
- Use pread()/write() for synchronous I/O.
+ This supports regular as well as vectored pread() and pwrite()
+ commands.
+ **block**
+ This is the same as psync except that it also supports zone
+ management commands using Linux block layer IOCTLs.
.. option:: xnvme_admin=str : [xnvme]
Select the xnvme admin command interface. This can take these values.
**nvme**
- This is default and uses linux NVMe Driver ioctl() for admin commands.
+ This is default and uses linux NVMe Driver ioctl() for admin
+ commands.
**block**
Use Linux Block Layer ioctl() and sysfs for admin commands.
- **file_as_ns**
- Use file-stat to construct NVMe idfy responses.
.. option:: xnvme_dev_nsid=int : [xnvme]
- xnvme namespace identifier, for userspace NVMe driver.
+ xnvme namespace identifier for userspace NVMe driver, such as SPDK.
.. option:: xnvme_iovec=int : [xnvme]
appended, the total error count and the first error. The error field given
in the stats is the first error that was hit during the run.
+ Note: a write error from the device may go unnoticed by fio when using
+ buffered IO, as the write() (or similar) system call merely dirties the
+ kernel pages, unless :option:`sync` or :option:`direct` is used. Device IO
+ errors occur when the dirty data is actually written out to disk. If fully
+ sync writes aren't desirable, :option:`fsync` or :option:`fdatasync` can be
+ used as well. This is specific to writes, as reads are always synchronous.
+
The allowed values are:
**none**
projects / fio.git / blobdiff