[linux-lvm] raid & its stripes

[lejeczek]

On 14/09/17 15:58, Brassow Jonathan wrote:
> Seems strange on the surface.  Would you mind posting the layout of each?  ‘lvs -a -o +devices’
>
>   brassow
here is for LV created without -i, both times with & without 
I supplied all ten(all that VG has) pvs as arguments to 
lvcreate.

$ lvs -a -o +devices,stripes,stripe_size chenbro0.1
   LV                 VG         Attr       LSize  Pool 
Origin Data% Meta%  Move Log Cpy%Sync Convert 
Devices                                 #Str Stripe
   raid0.A            chenbro0.1 rwi-aor--- 21.18t 
raid0.A_rimage_0(0),raid0.A_rimage_1(0)    2 16.00k
   [raid0.A_rimage_0] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdak(0)                               1     0
   [raid0.A_rimage_0] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdam(0)                               1     0
   [raid0.A_rimage_0] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdao(0)                               1     0
   [raid0.A_rimage_0] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdaq(0)                               1     0
   [raid0.A_rimage_0] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdas(0)                               1     0
   [raid0.A_rimage_0] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdau(0)                               1     0
   [raid0.A_rimage_1] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdal(0)                               1     0
   [raid0.A_rimage_1] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdan(0)                               1     0
   [raid0.A_rimage_1] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdap(0)                               1     0
   [raid0.A_rimage_1] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdar(0)                               1     0
   [raid0.A_rimage_1] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdat(0)                               1     0
   [raid0.A_rimage_1] chenbro0.1 iwi-aor--- 10.59t 
/dev/sdav(0)                               1     0

I cannot remove this LV for a while thus will not be able to 
recreate with -i for now, sorry.

>> On Sep 13, 2017, at 8:53 AM, lejeczek <peljasz at yahoo.co.uk> wrote:
>>
>> hi boys, girls
>>
>> man page reads: -i ...This is equal to the number of physical volumes to scatter the  logical  volume data....
>> I wonder, when I do not use -i while creating an LV with 10 phy devs.
>>
>> $ lvcreate -n raid0.A --type raid0 -I 16 -l 97%pv
>>
>> a dbench would show:
>> $ dbench -t 60 20
>> ...
>> Throughput 112.309 MB/sec  20 clients  20 procs  max_latency=719.409 ms
>>
>> Yet when I say: this many stripes:
>>
>> $ lvcreate -n raid0.A --type raid0 -I 16 -i 10 -l 97%pv
>>
>> dbench:
>> ...
>> Throughput 83.2822 MB/sec  20 clients  20 procs  max_latency=816.027 ms
>>
>> And though the results would vary, xfs, a dbench for LV with no -i as an argument(which LVM chooses then to be 2) would always look better.
>> And I thought, as in the manual, always make stripes to go to all phy devices.
>>
>> Question - is there some "little" magic LVM does? And if yes then how/what it is?
>> many thanks, L.
>>
>> .
>>
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>
> _______________________________________________
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