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
