I came across an interesting problem that I'd like to share in case anyone else is unfortunate enough to have the same problem.
Customer has a large deployment of HP thin client t5740e across many sites. Most of these sites the devices are working fine, but suddenly we found that for some new sites, the performance was really bad. Everything was the same in terms of hardware, drivers, software and Aruba configuration.
After much testing and packet captures, I suddenly realised (a bit of a eureka moment) that the devices were showing 2 stream capability, when they only had one antenna.
(controller) #show ap association essid wifi
Flags: W: WMM client, A: Active, K: 802.11K client, B: Band Steerable
PHY Details: HT: High throughput; 20: 20MHz; 40: 40MHz
<n>ss: <n> spatial streams
Association Table
-----------------
Name bssid mac auth assoc aid l-int essid vlan-id tunnel-id phy assoc. time num assoc Flags
---- ----- --- ---- ----- --- ----- ----- ------- --------- --- ----------- --------- -----
AP060 00:24:6c:61:73:12 70:f1:a1:e7:87:3c y y 2 1 wifi 36 0x10c5 a-HT-40sgi-2ss 7d:11h:49m:40s 1 WAB
AP15 00:24:6c:61:73:52 70:f1:a1:94:fa:fa y y 1 1 wifi 36 0x10f1 a-HT-40sgi-2ss 2d:2h:52m:5s 2 WA
AP02 00:24:6c:61:72:91 70:f1:a1:94:f9:cd y y 1 1 wifi 36 0x10fa a-HT-40sgi-2ss 4d:20h:53m:14s 1 WAB
Ping tests to any of these clients showing 2ss results in loss of 10-12%, whereas to one of these clients with 1ss results in 0% loss. A raw download test will show up to a 10 fold increase in speed when they use only 1 stream.
Changing the ht-ssid-profile to have a supported mcs set of 0-7 was an effective workaround in forcing these clients to only use 1 stream.
Driver version 9.2.0.480 from HP also disables the client advertising 2 streams. I tested on a client connected to AP with default config of mcs set 0-23 and indeed they connected showing only 1 stream.
Hopefully this will avoid anyone else going through the same pain I had to endure.
:smileyhappy: