On 21 March 2012 02:08, Shaohua Li <shli@xxxxxxxxxx> wrote: > 2012/3/20 Shaohua Li <shli@xxxxxxxxxx>: >> 2012/3/20 Holger Kiehl <Holger.Kiehl@xxxxxx>: >>> Hello, >>> >>> >>> On Tue, 20 Mar 2012, Shaohua Li wrote: >>> <snip> > Thanks for the testing. The trace data is very helpful. In the intel > SSD, trace data > shows a discard request uses about 1 ~ 3 ms. The filesystem suffers from > fragmentation too, so lots of small discard requests. When ext4 starts doing > discard, it usually uses more than 1 minutes. That's too bad. > If just looking one disk's trace data, there are some extra latencies between > two discard requests. The combined trace data of two disks show the latency > comes from waiting for another disk, so nothing abnormal. I thought we could > do an optimization for this case in the future. > So in summary, discard from the SSDs is slow. When your filesystem is > fragmented, the performance will be terrible. > > Thanks, > Shaohua > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html Many people prefer to have the filesystems mounted without discard, then they run a TRIM command/script at night (or whenever the disk isn't used very much). This way the TRIM commands don't slow down the 'overall' performance. Mathias -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
