[linux-lvm] stripped LV with segments vs one segment

[Zdenek Kabelac]

Dne 10.4.2017 v 13:16 lejeczek napsal(a):
>
>
> On 10/04/17 12:03, Zdenek Kabelac wrote:
>> Dne 10.4.2017 v 11:29 lejeczek napsal(a):
>>> hi there
>>>
>>> I could not extend my stripped LV, had 3 stripes and wanted to add one more.
>>> Only way LVM let me do it was where I ended up with this:
>>>
>>>   --- Segments ---
>>>   Logical extents 0 to 751169:
>>>     Type        striped
>>>     Stripes        3
>>>     Stripe size        16.00 KiB
>>>     Stripe 0:
>>>       Physical volume    /dev/sdd
>>>       Physical extents    0 to 250389
>>>     Stripe 1:
>>>       Physical volume    /dev/sde
>>>       Physical extents    0 to 250389
>>>     Stripe 2:
>>>       Physical volume    /dev/sdc
>>>       Physical extents    0 to 250389
>>>
>>>   Logical extents 751170 to 1001559:
>>>     Type        linear
>>>     Physical volume    /dev/sdf
>>>     Physical extents    0 to 250389
>>>
>>> 1st question - was this really the only way LVM would extend?
>>> 2nd - is there performance penalty with segments like above vs one stripped
>>> segment?
>>>
>>
>> Hi
>>
>>
>> Not really sure what you aim to do.
>>
>> If you have LV segment with 3 stripes - you have to keep also extension
>> using 3 stripes -  you can't  have 1st. halve of LV spanning 3 disk and add
>> there a new LV segment as linear - as listed in this post.
>>
>> Both segments must by striped.
>>
>> Regards
>>
>> Zdenek
>
> I had 3 stripe LV, you know, three PVs, and wanted the LV to have 4 stripes,
> wanted to add 4th PV, you can see it from above lvdisplay.
> I tried these and each time it errored:
> $ lvextend -v -i 4 -l+100%free dellH200.InternalB/0
> $ lvextend -v -i 4 -l+100%pv dellH200.InternalB/0 /dev/sdf

You can't request stripe 4  (needs 4 disks)  and pass just single  /dev/sdf 
device.


Zdenek