On 03/02/2013 06:48 PM, Stan Hoeppner wrote: > On 3/2/2013 11:07 AM, Phil Turmel wrote: >> On 03/02/2013 04:15 AM, Stan Hoeppner wrote: >>> On 3/1/2013 10:06 AM, Adam Goryachev wrote: > ... >>>> Is it worth reducing the chunk size from 64k down to 16k or even smaller? >>> >>> 64KB chunks should be fine here. Any gains with a smaller chunk would >>> be small, and would pale in comparison to the amount of PITA required to >>> redo the array and everything currently sitting atop it. Remember you'd >>> have to destroy it and start over. You can't change chunk size of an >>> existing array. >> >> Actually, you can. For levels 0 and 4,5,6. > > First, I'll reiterate that a smaller chunk size likely is not going to > yield real workload gains for Adam. And it obviously would decrease his > FIO numbers, making him think performance decreased, even if it actually > increased slightly with his real workload. No contest. I have effectively no experience at these hardware performance levels. > Speaking strictly now from a knowledge transfer standpoint, does this > chunk size change feature go back a ways or does it require a fairly > recent kernel and/or mdadm? Are there any prerequisites or special > considerations different from any other reshape operation? >From the announcement for mdadm version 3.1, October 2009: > It contains significant feature enhancements over 3.0.x > > The brief change log is: > - Support --grow to change the layout of RAID4/5/6 > - Support --grow to change the chunksize of raid 4/5/6 > - Support --grow to change level from RAID1 -> RAID5 -> RAID6 and > back. > - Support --grow to reduce the number of devices in RAID4/5/6. > - Support restart of these grow options which assembling an array > which is partially grown. > - Assorted tests of this code, and of different RAID6 layouts. > > Note that a 2.6.31 or later is needed to have access to these. > Reducing devices in a RAID4/5/6 requires 2.6.32. > Changing RAID5 to RAID1 requires 2.6.33. So I'm sure there are plenty of older systems that can't do this, but current distros should all have it. Phil -- 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
