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The paper has other locality concerns which apply to all SSDs: “Locality is not only valuable for reducing required RAM for translations, but also for other pu
by dan-robertson 5y ago
The paper has other locality concerns which apply to all SSDs:
“Locality is not only valuable for reducing required RAM for translations, but also for other purposes. For example, all types of SSDs are sensitive to locality due to their data cache. In addition, for SSDs that arrange flash chips in a RAID-like fashion, writes with good locality are more likely to update the same stripe and the parity calculation can thus be batched and written concurrently [92], improving performance.”
- wtallis 5y agoSSDs don't have much data caching. They use the large amount of DRAM for metadata (the FTL), and have small amounts of write buffering. Read caching and prefetching tends to be minimal and amount to the page buffers on each plane of each die, ie. the hardware has to perform a read of 16kB even if you only ask for 4kB. The bit about updating the same stripe also sounds like hard drive talk, where data can be updated in-place. It doesn't make sense in an SSD context where all modifications go to new stripes and the drive will readily combine a batch of writes to disparate LBAs into a burst of writes to contiguous physical pages. There's just not much truth behind the Locality rule that isn't already covered by the Request Scale rule.