SSD align test

Simple program to test read/write speed of your SSD partition to check if it's aligned correctly.

Methodology

Since SSDs have write and erase block sizes correspondingly) much larger than a sector size (around 4K and 256-512K correspondingly), incorrectly aligned partitions will result in so-called write amplification, which means degraded performance and increased wear rate.

It is therefore important to align partition boundaries correctly, and this utility helps to confirm that, or determine correct alignment.

The utility performs a set of tests. Each tests reads and/or writes the same number of blocks of specified size at specified intervals, and each other test incorporates additional offset (usually sector size). Throughput of each test is then calculated.

Currently, the program only prints resulting throughput rates to be evaluated by the user.

Usage

./ssdaligntest [-rw] [-b block-size] [-i interval-size] [-s offset-step] [-c count] [-k skip-count] file

• -r - read blocks during the test
• -w - write blocks during the test (destructive!)

At least one of above options is required. If only -w is specified, zeroes are written to the target file (which is destructive!), if both -r and -w are specified, the same blocks which are read are written back.

• -b - read/write block size in bytes
• -i - interval size in bytes
• -s - offset step for each test in bytes
• -c - number of blocks to read/write
• -k - number of blocks to skip (useful to counter caching)
• file - usually device node for your disk or partition

Example

Here's an example of running read test on some SSD partition. You can see offsets which are multiple of 4096 bytes giving better read performance, and since the partition begins with a "fast" offset it's correctly aligned.

./ssdaligntest -r -b 4096 -i 8192 -s 512 -c 10000 /dev/ada0p1
test 16/16 (offset 7680)...
OFFSET     DURATION      THROUGHPUT
     0       1.51 s      25.93 MB/s <--
   512       1.95 s      20.04 MB/s
  1024       1.95 s      20.04 MB/s
  1536       1.95 s      19.99 MB/s
  2048       1.95 s      20.03 MB/s
  2560       1.95 s      20.02 MB/s
  3072       1.95 s      20.01 MB/s
  3584       1.96 s      19.95 MB/s
  4096       1.50 s      25.99 MB/s <--
  4608       1.73 s      22.54 MB/s
  5120       1.73 s      22.55 MB/s
  5632       1.73 s      22.54 MB/s
  6144       1.73 s      22.54 MB/s
  6656       1.74 s      22.42 MB/s
  7168       1.74 s      22.39 MB/s
  7680       1.76 s      22.21 MB/s
The partition looks to be aligned

Author

• Dmitry Marakasov amdmi3@amdmi3.ru

License

• 2 clause BSD. See COPYING file.