Future Unraid


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It is not that simple as SSD's are not consistent on how they handle sectors after a trim (erase) operation.     If they can be guaranteed to return all zeroes on reading such a sector (called 'deterministic read zero after trim' aka RZAT) then they will already work in the array.   However if they do not then it is impossible to maintain a valid parity with the way that Unraid currently works.   Also, some SSD's that DO work in RZAT fashion do not actually report this in their capabilities.  Whether changes to the low level device handling within Unraid can ever resolve this I am not sure.

 

There is also the fact that not all HBA's support trim operations in the first place.   If the HBA does not support trim then the performance of an SSD can degrade significantly over time.  Again there is no consistency here as it appears some SSD's have the equivalent to trim built into their firmware so do not need the host to do it explicitly.

 

It is this lack of consistency that has held up the idea of SSD's in the array being an officially supported feature.  Users who have purchased SSD's that do support RZAT capability have already experimented with SSDs in arrays and they appeared to operate correctly.    You will also get way with using SSDs without RZAT capability if you do not have any parity drives - but this is not the way most users expect to work.

Edited by itimpi
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