2 ms·
wear levelling isn't really copy on write is it? the original block will be removed from the mapping entirely (not referred to by a copy)
by blibble 5y ago
wear levelling isn't really copy on write is it?
the original block will be removed from the mapping entirely (not referred to by a copy)
- londons_explore 5y agoTypically flash devices can't overwrite data directly, and can only erase very large blocks (ie. 1MB or more). That means any write of data must be made to a new, freshly erased, location. The old version of the data, sitting in the middle of a large eraseblock is no longer used, but cannot be reused until everything else in the eraseblock is either unused or copied elsewhere. In the worst case (of a nearly full SSD), it means that for every 1 byte write into a 4k page, a full 1Mbyte of data needs to be copied. Typical cases are better (when the drive has plenty of spare space, so can delay the reclamation of the eraseblock for as long as possible, hoping that other things in the block are invalidated, reducing the amount that needs to be copied). TL;DR: It's complex, but a lot of copying is involved with most writes...