I know it's bad. I'm trying to determine the cause of the difference, and if it's a "feature" of that SSD or a bug of some sort. I'll check if the speed changes when I disable barrier on the mounted filesystem. If so then it's slow on write barriers.
2014-03-24 1:35 GMT+01:00 Simon Slavin <slav...@bigfraud.org>: > > On 23 Mar 2014, at 11:19pm, piotr maliński <riklau...@gmail.com> wrote: > > > So maybe this particular SSD is slow with write barriers, while other > > doesn't have a problem with it (as they don't change performance between > > SATA and USB3). > > You have missed the point. When Florian write "Many USB SATA adapters do > not handle [write barriers] correctly" he is saying that your storage > medium will corrupt your data if power fails or other hardware problems > occur before the files are not closed correctly. Write barriers are > important. > > SQLite tries very hard to make sure your data is safe. Doing this > involves a number of 'write' commands which have to be done in a specific > order. Rotating disk drives are very slow to do this because they have to > wait for the disk to rotate to the right position each time. SSD storage > is faster because any sector can be written at any time, but they still > should be accepting each 'write' command, then doing it, then returning a > result of 'write successful'. In other words, they should not be able to > say "command executed" immediately. They should have a write barrier. > > If you find some storage system that is unexpectedly fast, it is probably > not doing this correctly. It is accepting the 'write' command, immediately > saying that the command was successful, but actually doing the 'write' > command in the background later. Most desktop computers are deliberately > set up to do this because it makes the computer run faster, and that's what > users want. And most storage systems that do this do not do the writes in > the order the commands were given. They blast all the writes to storage in > sector order, because this gives, overall, a faster result. > > And that's why hard disks sold to be used in servers apparently run more > slowly: they are set to do storage properly, because they are more likely > to be used to store valuable data rather than just write a document or > email which can be retyped if changes are lost. > > So yes, one drive system is running quickly. But it's doing it at the > cost of corrupting your data if you suffer a hardware problem. You have > lost the ACID property of your database. If you want to know that your > data is safe, you're probably going to want the system that runs slowly. > > On the other hand, that particular type of SSD may just have timings > slightly different from what the storage system expects. > > Simon. > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
