I just thought that is some interesting Meta, when you plan a new System and you got the option, maybe make all the drives the same size and speed, grabbing every drive you got in the basement somewhere just to have a few more GBs is maybe not the best idea, long term. A disk dies, you replace it and snapraid restores the lost data to the new disk. As long as you only encounter a single disk failure this is perfectly fine. Consider the scenario where you have X number of data disks and a single parity. To create a three-way mirror space, specify 3 for the NumberofDataCopies parameter or 2 for the PhysicalDiskRedundancy parameter. currently i don't have any bigger HDDs than 2TB in there. As David already stated, snapraid allows you to use any combination of parity and data disks you want. By default, when you specify Mirror, Storage Spaces creates a two-way mirror, and when you specify Parity, Storage Spaces creates a single-parity space. Same effect when the 1TB disks get closer to the end and then at 2TB again. For example i got a old 500GB disk in there, the further the parity check closes in on 500GB the slower the read speed gets (down to ~75MB/s), once the 500GB are read and the Disk is done, the parity check speeds up again (150MB/s). I also noticed, since i have drives with different sizes, when you do a parity check, the smallest drive will bottleneck the entire system, because all drives need to read the same positions at the same time and the further to the end any disk gets, it gets slower. (unless you do some funky stuff with cache drives of course) So yes, the parity disk being the fastest would be the ideal situation, especially if you have lots of different size and speed drives. So if you have a data disk that is faster than the parity disk it will be bottlenecked by it. I have all different drives in my array and from my observations, when writing to a share, the data disk and the parity disk will both be reading and writing at the same time.
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