Re: AWFUL reshape speed with raid5.
flat view
From: Justin Piszcz <hidden>
Date: 2008-07-30 17:08:04
On Wed, 30 Jul 2008, Jon Nelson wrote:
On Wed, Jul 30, 2008 at 11:23 AM, Bill Davidsen [off-list ref] wrote:quoted
Jon Nelson wrote:quoted
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?
In dstat, the speed is doubled for the total for some reason, divide by 2 (if you compare with iostat -x -k 1) you should see the difference. As far as the grow itself, the last time I did it was 2-3 years ago but if I recall it ran for 24hrs+ (IDE system, PCI, etc) between 5-15MiB/s. Justin.