Quoth [email protected]: > Allow me to disagree. Arenas are, mostly, append-only. Index is write-random. For each clump about 40 bytes are changed at random locations. Therefore, you are are safe filling up the arena disc entirely, but the index disc will be weared up, for nothing. Most ssd vendors recommend using a very low percentage of nominal capacity for mit use cases.
> for each clump, about 40 bytes are changed Average clump size is on the order of 10KiB, or ~20 sectors. Looking at orders of magnitude, we're talking about roughly one (random) sector written to the index for every 20 (sequential) sectors written to the arena. Moreover, arena writes ALSO have random writes! Each write to the arena, in addition to the sequential clump, seeks to the end of the arena to add the index entry so that, if the index dies, it can be rebuilt without scanning the actual data area. There should be one of those for each write to the index. Yes, the index write is _more_ random, but there's also _so few of them_ that it shouldn't matter. keep in mind as well that the index is intended to be sized such that it never hits 100% of usage. If you have actual data to show that this is a problem, I'm happy to take a look, but it seems to be speculative and based on ideas of how SSDs _should_ work, not based on any actual SSD that you can point to and say "look, its worn out in less than a year from being used as an index"? ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/T4d8ba4236feb5d92-Mafd2cbacdf7b4c1799ce1c77 Delivery options: https://9fans.topicbox.com/groups/9fans/subscription
