Filesystem Tuning

Tips for RedHat filesystem tuning.

– Optimize file system block size.
Block size is selected at mkfs time. If you plan on storing mostly smaller or larger files than the default block size,
then decrease or increase the block size of the filesystem during mkfs time. This will allow for less wasted space and
also for faster reads when the file size fits in a single block.

# tune2fs -l /dev/mapper/vg_hv1-lv_home | grep 'Block size'
Block size:               4096 (bytes)

– Match filesystem geometry to storage subsystem.
During mkfs time, align the geometry of the filesystem with that of the RAID sub-system.
This might be set automatically, but it does not hurt to check. As per RedHat “For striped block devices (for example, RAID5 arrays), the stripe geometry can be specified at the time of file system creation. Using proper stripe geometry greatly enhances the performance of an ext4 file system…
For example, to create a file system with a 64k stride (that is, 16 x 4096) on a 4k-block file system, use the following command:”

# mkfs.ext4 -E stride=16,stripe-width=64 /dev/device

– External journals
If you are using a journaling filesystem such as ext4, move the journal to a faster disk that the data.
This will speed up journal writes and make your writes faster. Journals are specified at mkfs time.

# mke2fs -O journal_dev

– Use the ‘nobarrier’ option when mounting filesystems.
Barriers is a way of ensuring that filesystem metadata is written correctly on persistent storage.
This will slow down filesystems that have fsync() being used excessively.
If you disable barriers you risk corruption of data in case of power loss, however the risk might be worth it
if data is redundant on other systems.

– Disable access time, using the ‘noatime’ mount option in /etc/fstab.
File access time is updated when it is read, you may not need this to ‘feature’.
in RHEL relatime behavior updates atime only if atime is older than mtime or ctime.
Enabling noatime also enables nodiratime.

– Increased read-ahead support
Read-ahead speeds up file access by pre-fetching data into the page cache.
Get current value using ‘blockdev -getra device’.
Change the value using ‘blocdev -setra N device’.
N is the number of 512-byte sectors.

# blockdev --getra  /dev/mapper/vg_hv1-lv_root
1024

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