Articles: Storage
 

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Now let’s check the situation with enabled WB-caching:

At first sight the graphs look a little worse than in case of WriteThrough-caching: they are pretty curved and not that nice and smooth any more. However, if we consider absolute values, then the performance will be higher during small data blocks processing, and at least not lower during larger data blocks processing. Even though each graph has a spot or two where the performance drops down compared with what we saw in case of WT, we can still conclude that WB-caching has overall positive influence on the performance of RAID 0 and JBOD during linear reading of small data blocks, and hardly has any influence on the large data blocks read speed at all.

The use of WB-caching increases the performance of mirrored arrays when the processed data blocks are smaller than 8KB. If we are reading large data blocks then WB-caching doesn’t affect the read speed at all.

As a result, a single HDD and RAID 1 array demonstrate similar read speed for smaller than 8KB data blocks. As the data blocks grow bigger, the HDD speed starts to act as a limiting factor, so that the influence of WB-caching disappears.

Now let’s have a look at sequential writing:

 
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