cifs performance troubleshooting

[_hunter]

Greetings,

I'm having pretty poor performance with remote storage (located in Azure), attached via CIFS:

$ rsync -ah --info=progress2 /mnt/aptly/public/ /tmp/tmp.u5CSfrrFut
       591.44M 100%    4.35MB/s    0:02:09 (xfr#701, to-chk=0/1029)

that's what 'mount' says about this share:

//ABC.file.core.windows.net/aptly on /mnt/aptly/public type cifs (rw,relatime,vers=2.1,sec=ntlmssp,cache=none,username=DEF,domain=X,uid=0,noforceuid,gid=0,noforcegid,addr=XYZ,file_mode=0777,dir_mode=0777,nounix,serverino,mapposix,rsize=1048576,wsize=1048576,echo_interval=60,actimeo=1)

I found 'cifsiostat' utility, which supposed to answer some of my questions, but by some reason it displays nothing:

$ cifsiostat
Linux 4.9.0-8-amd64 (aptly)        07/12/19        _x86_64_        (1 CPU)

Filesystem:                    rB/s         wB/s    rops/s    wops/s         fo/s         fc/s         fd/s

I enabled 'sysstat', as described here:
tecadmin.net/sysstat-monitor-linux-system-performance/
What is strange: according to man:
manpages.debian.org/unstable/sysstat/cifsiostat.1.en.html
-- such file: "/proc/fs/cifs/Stats" should exist, but I have only this 6 files in that dir

$ ls -la /proc/fs/cifs
total 0
dr-xr-xr-x 2 root root 0 Jul 12 13:51 .
dr-xr-xr-x 7 root root 0 Jul 11 12:00 ..
-r--r--r-- 1 root root 0 Jul 12 13:51 DebugData
-r--r--r-- 1 root root 0 Jul 12 13:51 LinuxExtensionsEnabled
-r--r--r-- 1 root root 0 Jul 12 13:51 LookupCacheEnabled
-r--r--r-- 1 root root 0 Jul 12 13:51 SecurityFlags
-r--r--r-- 1 root root 0 Jul 12 13:51 cifsFYI
-r--r--r-- 1 root root 0 Jul 12 13:51 traceSMB

So, basically, I'm looking for any help in understanding why I'm having such poor results.

Best regards...