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Let’s turn to sequential write now:

And the graphs:

Here you go: these are the first problems for today. The speed of 4-HDD RAID0 array is indecently low on big requests. It seems like the controller lacks cache memory in these circumstances. Well, it is overall weird to have a situation when one drive of the array has four times the amount of the controller’s cache memory…

The performance of RAID1 array nearly coincides with that of the single drive, while the speed of RAID10 is a little lower than that of the two-disk RAID0. It’s more complicated with the write speed of RAID5 arrays. When the data blocks are small, the write speed of RAID5 is higher than that of a single drive or of the “mirror”. This is where R5 Fusion works (it “glues” write requests together in the controller cache). But when the requests are big, there is simply not enough space in the controller cache…

By disabling lazy write we greatly reduce the performance of every array; this is especially catastrophic for the RAID5!

 
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