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NAS - Build a Linux NAS - Tune the System

There are many settings that can be tuned.

As there are many factors than can affect tuning performance, it is recommended to perform a number of tests using different figures to determine the optimum values:

Create a test file that will be used for reading and writing tests.
Perform each test using dd.
```
dd if=testfile of=/dev/null bs=8k
```
Between each test, clear the OS disk cache.
```
sync;echo 3 > /proc/sys/vm/drop_caches
```

NOTE: Vary the size of the test file depending on how much RAM the system has.

It is suggested to have the test file be large, such as 32G.
Consider changing the blocksize used with dd to a larger value, say bs=16k, if there is a lot of RAM.

Tuning stripe_cache_size

stripe_cache_size affects RAM used by mdadm for writing of data.

Ubuntu default value is 256.

Verify the current value:

cat /sys/block/md0/md/stripe_cache_size

Change it:

echo *number* > /sys/block/md0/md/stripe_cache_size

NOTE: Test with different sizes.

Test with stripe_cache_size=256
Test with stripe_cache_size=512
Test with stripe_cache_size=1024
Test with stripe_cache_size=2048
Test with stripe_cache_size=4096
Test with stripe_cache_size=8192
Test with stripe_cache_size=16384
Test with stripe_cache_size=32768

At each test, check the Write performance, for example:

dd if=testfile of=/dev/null bs=8k
361680+0 records in
361680+0 records out
2962882560 bytes (3.0 GB) copied, 0.92471 s, 3.2 GB/s

Tuning Read Ahead

Changing the read ahead value should impact read performance.

Default read ahead value is 1536.

Change it::

blockdev --setra *number* /dev/md0

NOTE: Test with different sizes.

Test results with Read Ahead @ 1536
Test results with Read Ahead @ 4096
Test results with Read Ahead @ 32768
Test results with Read Ahead @ 262144
Test results with Read Ahead @ 524288

At each test, check the Read performance, for example:

dd if=testfile of=/dev/null bs=8k
361680+0 records in
361680+0 records out
2962882560 bytes (3.0 GB) copied, 0.92471 s, 3.2 GB/s

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Table of Contents

NAS - Build a Linux NAS - Tune the System

Tuning stripe_cache_size

Tuning Read Ahead