IO values for i7ie.2xlarge are identical to i7ie.xlarge

[mykaul]

i7ie.xlarge:
  read_iops: 117257
  read_bandwidth: 1148572714
  write_iops: 94180
  write_bandwidth: 505684885
i7ie.2xlarge:
  read_iops: 117257
  read_bandwidth: 1148572714
  write_iops: 94180
  write_bandwidth: 505684885

Whereas https://docs.aws.amazon.com/ec2/latest/instancetypes/so.html#so_instance-store says:

i7ie.large	1 x 1250 GB	NVMe SSD	54,166 / 43,333		✓
i7ie.xlarge	1 x 2500 GB	NVMe SSD	108,333 / 86,666		✓
i7ie.2xlarge	2 x 2500 GB	NVMe SSD	216,666 / 173,332		✓

So double the performance between them.

Originally posted by @mykaul in #559

[roydahan]

@syuu1228 is it just a copy-paste error or these are the values we get for i7ie.2xlarge?

[syuu1228]

Here are raw values of i7ie iotune results, it executed 3 times on each instances, and averages are shown at the bottom.
It seems i7ie.large uses slowest SSD, i7ie.xlarge and i7ie.2xlarge using medium speed SSD, and larger instances (3xlarge, 6xlarge, 12xlarge...) using fastest SSD.
So I decided copy i7ie.xlarge parameters to i7ie.2xlarge.

instance_type   read_iops       read_bandwidth  write_iops      write_bandwidth
i7ie.large.0    58450   574886272       47148   253077216
i7ie.large.1    58447   574871872       47144   253152960
i7ie.large.2    58452   574805824       47145   253168576
i7ie.xlarge.0   117261  1148629760      94184   505675680
i7ie.xlarge.1   117253  1148723072      94177   505678784
i7ie.xlarge.2   117257  1148365312      94181   505700192
i7ie.2xlarge.0  117266  1148608256      94166   505745536
i7ie.2xlarge.1  117270  1148134016      94161   505677120
i7ie.2xlarge.2  117266  1148369024      94177   505698688
i7ie.3xlarge.0  352843  3422118400      119127  1526412672
i7ie.3xlarge.1  352844  3421702144      118973  1526431104
i7ie.3xlarge.2  352817  3424049152      119881  1526483456
i7ie.6xlarge.0  352813  3432191232      118808  1526523520
i7ie.6xlarge.1  352837  3424704512      119741  1526485376
i7ie.6xlarge.2  352822  3428499456      119246  1526491136
i7ie.12xlarge.0 352835  3422241280      119566  1526699136
i7ie.12xlarge.1 352829  3425162240      119214  1526719872
i7ie.12xlarge.2 352832  3424160000      118033  1526715776
i7ie.18xlarge.0 352825  3425764608      119544  1526821376
i7ie.18xlarge.1 352816  3425155072      119555  1526833664
i7ie.18xlarge.2 352815  3428421120      119518  1526809088
i7ie.24xlarge.0 352824  3424752128      119147  1526504320
i7ie.24xlarge.1 352832  3422750976      119154  1526500992
i7ie.24xlarge.2 352826  3424811008      119535  1526532480
i7ie.48xlarge.0 352834  3423049728      119516  1526578176
i7ie.48xlarge.1 352831  3424246016      119574  1526628352
i7ie.48xlarge.2 352815  3428381440      119226  1526603392

i7ie.large      58449   574854656       47145   253132917
i7ie.xlarge     117257  1148572714      94180   505684885
i7ie.2xlarge    117267  1148370432      94168   505707114
i7ie.3xlarge    352834  3422623232      119327  1526442410
i7ie.6xlarge    352824  3428465066      119265  1526500010
i7ie.12xlarge   352832  3423854506      118937  1526711594
i7ie.18xlarge   352818  3426446933      119539  1526821376
i7ie.24xlarge   352827  3424104704      119278  1526512597
i7ie.48xlarge   352826  3425225728      119438  1526603306

I just ran iotune on i7ie.2xlarge again to make sure current parameter is correct, result was:

disks:
  - mountpoint: /var/lib/scylla
    read_iops: 117258
    read_bandwidth: 1150152192
    write_iops: 94138
    write_bandwidth: 508599840

Seems like result is unchanged, it almost same performance as i7ie.xlarge.

These results don't seem to match Amazon's documentation, but isn't the parameters that Amazon's documentation indicates are the sum of all drives?
If it correct, probably it seems to match our measurements.

[roydahan]

Sounds ok to me.
We will know the real effect only when running performance tests on these instance types, but I don't think it's necessary right now.
we may want @avikivity or @xemul to approve that.