HDD Surface Scanner ‒ tests description

HDD Surface Scanner in current vesrion 0.5 enables to perform three types of tests: Tests investigate selected range of memory (params "LBA start" and "LBA end"). Implicitely they are set to cover the whole memory device.

Sequential read test

Test reads sequentially selected memory device, implicitely per 128 kB. HDD Surface Scanner evaluates: Size of blocks read together is set by parameter "Block Read Together", where 1 block represents 512 Bytes. We recommend this test to check memory devices. Since it tests the whole memory range, it provides a good information about the device state.

Random read test

During this test, memory blocks of selected size are accessed in a random manner. In particular if the tested range of memory device is s and block b was read last time, the next block is selected in such a way, that it is in distance at least s / 4 from b. The size of blocks read together is set by parameters "Block Read Together" as in case of Sequential read test. Please notice that this test may reduce a lifetime of clasic HDDs, since it enforces quick movements of head inside HDD.
The plot depicting the speed of reading uses block addressing as axis X. Thus the shape of curve is changing in time from linear estimation (given just by two points) to wrinkled curve. An example is given in the following figures.
Random access test: plot with few measured points
Fig. 1: Random access test: plot with few measured points a short time after the test beginning
Random access test: more points are added to curve ...
Fig. 2: More points are added to curve during the test processing ...
Random access test: final result
Fig. 3: ... to get the final complex shape

(Sequential) read of each n-th block

Test goes through the selected range of memory in a sequential way similarly to "Sequential read test". The difference is that only the first 512 B are read during each memory access. More precisely, parameter "Block read together" value k implies test "jumping" per 512 × k Bytes: from these Bytes are read only first 512 B. Thus this test is quicklier than "Sequential read test", however the provided information is limited.