On Wed, Jul 30, 2008 at 11:23 AM, Bill Davidsen <davidsen@xxxxxxx> wrote: > Jon Nelson wrote: >> 2. If no I/O is taking place, why does it take so long? [ NOTE: I/O >> must be taking place but why doesn't vmstat show it? ] >> > > vmstat doesn't tell you enough, you need a tool to show per-device and > per-partition io, which will give you what you need. I can't put a finger on > the one I wrote, but there are others. I gave dstat a try (actually, I rather prefer dstat over vmstat...): This is right before, during, and after the --grow operation. --dsk/sdb-----dsk/sdc-----dsk/sdd-----dsk/sde----dsk/total- read writ: read writ: read writ: read writ: read writ 0 44k: 0 24k: 0 24k: 0 0 : 0 184k 0 0 : 0 0 : 0 0 : 0 0 : 0 0 0 24k: 0 0 : 0 0 : 0 0 : 0 48k 32M 14k: 32M 2048B: 32M 2048B: 0 0 : 191M 36k 63M 0 : 63M 0 : 63M 0 : 0 0 : 377M 0 65M 0 : 65M 0 : 65M 0 : 0 0 : 391M 0 72M 0 : 73M 0 : 73M 0 : 0 0 : 437M 0 74M 0 : 73M 0 : 74M 0 : 0 0 : 441M 0 70M 48k: 70M 0 : 70M 0 : 0 0 : 419M 96k 61M 44k: 61M 16k: 62M 32k: 0 0 : 368M 184k 71M 0 : 72M 0 : 71M 0 : 0 0 : 429M 0 74M 0 : 73M 0 : 73M 0 : 0 0 : 439M 0 73M 0 : 73M 0 : 73M 0 : 0 0 : 439M 0 71M 20k: 71M 0 : 71M 0 : 0 0 : 426M 40k 72M 0 : 72M 0 : 73M 0 : 0 0 : 434M 0 73M 0 : 74M 0 : 73M 0 : 0 0 : 442M 0 60M 40k: 59M 16k: 59M 28k: 0 0 : 356M 168k 73M 0 : 73M 0 : 73M 0 : 0 0 : 438M 0 70M 24k: 69M 0 : 70M 0 : 0 0 : 418M 48k 72M 0 : 71M 0 : 72M 0 : 0 0 : 430M 0 73M 0 : 73M 0 : 73M 0 : 0 0 : 437M 0 71M 0 : 71M 0 : 71M 0 : 0 0 : 427M 0 73M 0 : 73M 0 : 73M 0 : 0 0 : 437M 0 71M 24k: 71M 0 : 71M 0 : 0 0 : 428M 48k 72M 0 : 72M 0 : 72M 0 : 0 0 : 432M 0 73M 0 : 73M 0 : 73M 0 : 0 0 : 437M 0 71M 4096B: 70M 0 : 70M 0 : 0 0 : 422M 8192B 58M 0 : 58M 0 : 58M 0 : 0 0 : 350M 0 59M 24k: 60M 0 : 59M 0 : 0 0 : 357M 48k 74M 0 : 73M 0 : 74M 0 : 0 0 : 441M 0 19M 8192B: 19M 8192B: 19M 4096B: 0 0 : 114M 40k 0 0 : 0 0 : 0 0 : 0 0 : 0 0 0 0 : 0 0 : 0 0 : 0 0 : 0 0 0 160k: 0 16k: 0 20k: 0 0 : 0 392k So. Clearly, lots of I/O. 440MB/s total. Almost entirely reads. Question: to --grow --size the array, clearly we see lots of reads. Why aren't we seeing any (meaningful) writes? If there are no writes, then what purpose do the reads serve? -- 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
