I think test 2 actually makes dd allocate 1GB of memory and then write it to disk. So if you don't have 1GB free you may be testing your swap. Also, what kernel/btrfs version are you using? In what situations are you experiencing slowness? Wout. On Nov 18, 2010, at 7:19 , Magicloud Magiclouds wrote: > Hi, > Recently, I made a btrfs to use. And I met slowness problem. Trying > to diag it. I found this: > 1. dd if=/dev/zero of=test count=1024 bs=1MB > This is fast, at about 25MB/s, and reasonable iowait. > 2. dd if=/dev/zero of=test count=1 bs=1GB > This is pretty slow, at about 1.5MB/s, and 90%+ iowait, constantly. > May I know why it works like this? Thanks. > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
