Поддержка TRIM в Linux

Выдержка из Red Hat Enterprise Linux 6 Storage Administration Guide:

20.1. Deployment Considerations

Because of the internal layout and operation of SSDs, it is best to partition devices on an internal erase block boundary. Partitioning utilities in Red Hat Enterprise Linux 6 chooses sane defaults if the SSD exports topology information. This is especially true if the exported topology information includes alignment offsets and optimal I/O sizes.
However, if the device does not export topology information, Red Hat recommends that the first partition be created at a 1MB boundary.
In addition, keep in mind that logical volumes, device-mapper targets, and md targets do not support TRIM. As such, the default Red Hat Enterprise Linux 6 installation will not allow the use of the TRIM command, since this install uses DM-linear targets.
Red Hat also warns that software RAID levels 1, 4, 5, and 6 are not recommended for use on SSDs. During the initialization stage of these RAID levels, some RAID management utilities (such as mdadm) write to all of the blocks on the storage device to ensure that checksums operate properly. This will cause the performance of the SSD to degrade quickly.
At present, ext4 is the only fully-supported file system that supports TRIM. To enable TRIM commands on a device, use the mount option discard. For example, to mount /dev/sda2 to /mnt with TRIM enabled, run:

mount -t ext4 -o discard /dev/sda2 /mnt

By default, ext4 does not issue the TRIM command. This is mostly to avoid problems on devices which may not properly implement the TRIM command. The Linux swap code will issue TRIM commands to TRIM-enabled devices, and there is no option to control this behaviour.


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