System information

Contains current information on multiple-disk or RAID configurations on the system, if they
exist.
/p ro c/mo u n t s
Lists all mounts currently used by the system.
/p ro c/part it ions
Contains partition block allocation information.
For more information about the /pro c file system, refer to the Red Hat Enterprise Linux 6 Deployment
Guide.
2.4. Discard unused blocks
Batch discard and online discard operations are features of mounted file systems that discard blocks
not in use by the file system. They are useful for both solid-state drives and thinly-provisioned
storage.
Batch discard operations are run explicitly by the user with the fstri m command. This command
discards all unused blocks in a file system that match the user's criteria. Both operation types are
supported for use with ext4 file systems as of Red Hat Enterprise Linux 6.2 and later, so long as the
block device underlying the file system supports physical discard operations. This is also the case
with XFS file systems as of Red Hat Enterprise Linux 6.4 and later. Physical discard operations are
supported if the value of /sys/bl o ck/device/q ueue/d iscard _max_bytes is not zero.
Online discard operations are specified at mount time with the -o d iscard option (either in
/etc/fstab or as part of the mo unt command), and run in realtime without user intervention. Online
discard operations only discard blocks that are transitioning from used to free. Online discard
operations are supported on ext4 file systems as of Red Hat Enterprise Linux 6.2 and later, and on
XFS file systems as of Red Hat Enterprise Linux 6.4 and later.
Red Hat recommends batch discard operations unless the system's workload is such that batch
discard is not feasible, or online discard operations are necessary to maintain performance.
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