[dm-devel] raid1 round-robin scheduler

[Heinz Mauelshagen]

On 03/10/2015 12:55 PM, konstantin wrote:
>
>
> 19.02.2015 18:02, Heinz Mauelshagen пишет:
>>
>>
>> dm-mirror (i.e. "lvcreate --type mirror" or respective "dmsetup create
>> --table ...",
>> which is not the recommended raid1 layout any more) provides read
>> round-robin since long time.
>> You'd need an ancient kernel not to have it supported.
>>
>> "raid1"/"raid10" (the recommended targets) , i.e. the md-raid based
>> mappings accessible via the dm-raid target
>> do read optimizations as well. Use "lvcreate --type raid1/raid10 ..." or
>> a respective dm table to set
>> those up. The former ("raid1") is the default in modern distributions
>> and configurable via setting
>> 'mirror_segtype_default = "raid1"' in /etc/lvm/lvm.conf.
>>
>> Heinz
>>
>>
>>
>>
>> On 02/19/2015 08:23 AM, konstantin wrote:
>>> What version of the kernel should I use to get a round-robin read
>>> implementation on LV raid1?
>>>
>>
>> -- 
>> dm-devel mailing list
>> dm-devel at redhat.com
>> https://www.redhat.com/mailman/listinfo/dm-devel
>
> I'm create raid1 lv with "lvcreate --type raid1 -m1 -L5G -n r1lv r1vg" 
> on vg with two physical devices:
>
> lvs -a -o +devices
>   LV              VG   Attr     LSize Pool Origin Data%  Move Log 
> Copy%  Convert Devices
>   r1lv            r1vg rwi-a-m- 5.00g 100.00 
> r1lv_rimage_0(0),r1lv_rimage_1(0)
>   [r1lv_rimage_0] r1vg iwi-aor- 5.00g           /dev/sda(1)
>   [r1lv_rimage_1] r1vg iwi-aor- 5.00g           /dev/sdb(1)
>   [r1lv_rmeta_0]  r1vg ewi-aor- 4.00m           /dev/sda(0)
>   [r1lv_rmeta_1]  r1vg ewi-aor- 4.00m           /dev/sdb(0)
>
> but, reading is only one of the devices (i see nmon live disk 
> utilization). There are solutions to ensure reading from the two devices?
>

How do you test?
Do you read from multiple threads?