System information

As of Red Hat Enterprise Linux 6.4, ext4 and XFS are the only fully-supported file systems that
support d i scard . Previous versions of Red Hat Enterprise Linux 6 only ext4 fully supported
d i scard . To enable d i scard commands on a device, use the mo unt option d i scard . For
example, to mount /d ev/sd a2 to /mnt with d i scard enabled, run:
# mount -t ext4 -o discard /dev/sda2 /mnt
By default, ext4 does not issue the di scard command. This is mostly to avoid problems on devices
which may not properly implement the d i scard command. The Linux swap code will issue d i scard
commands to d iscard -enabled devices, and there is no option to control this behavior.
21.2. Tuning Considerat ions
This section describes several factors to consider when configuring settings that may affect SSD
performance.
I/O Scheduler
Any I/O scheduler should perform well with most SSD s. However, as with any other storage type, Red
Hat recommends benchmarking to determine the optimal configuration for a given workload.
When using SSDs, Red Hat advises changing the I/O scheduler only for benchmarking particular
workloads. For more information about the different types of I/O schedulers, refer to the I/O Tuning
Guide (also provided by Red Hat). The following kernel document also contains instructions on how
to switch between I/O schedulers:
/usr/share/d o c/kernel -version/D o cumentati o n/bl o ck/swi tchi ng -sched . txt
Virtual Memory
Like the I/O scheduler, virtual memory (VM) subsystem requires no special tuning. Given the fast
nature of I/O on SSD, it should be possible to turn down the vm_d i rty_backg ro und _rati o and
vm_d i rty_rati o settings, as increased write-out activity should not negatively impact the latency
of other operations on the disk. However, this can generate more overall I/O and so is not generally
recommended without workload-specific testing.
Swap
An SSD can also be used as a swap device, and is likely to produce good page-out/page-in
performance.
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