It seems I have to de-select the checkbox "Show available bricks from host" and so I can manually the the directory of the bricks

I see that bricks are mounted in /gluster/brick3 and that is the reason it does not show anything in "Brick Directory" drop down filed. If bricks are mounted under /gluster_bricks then it would have detected automatically. There is an RFE which is raised to detect bricks which are created manually.

BTW: I see that after creating a volume optimized for oVirt in web admin gui of 4.1.2 I get slight option for it in respect for a pre-existing volume created in 4.0.5 during initial setup with gdeploy.

NOTE: during 4.0.5 setup I had gluster 3.7 installed, while now I have gluster 3.10 (manually updated from CentOS storage SIG)

Making a "gluster volume info" and then a diff of the output for the 2 volumes I have:

new volume ==   <

old volume  ==    >

< cluster.shd-max-threads: 8

---

> cluster.shd-max-threads: 6

13a13,14

> features.shard-block-size: 512MB

16c17

< network.remote-dio: enable

---

> network.remote-dio: off

23a25

> performance.readdir-ahead: on

25c27

< server.allow-insecure: on

---

> performance.strict-o-direct: on

Do I have to change anything for the newly created one?

No, you do not need to change anything for the new volume. But if you plan to enable o-direct on the volume then you will have to disable/turn off remote-dio.

key=group,storage.owner-uid,storage.owner-gid,features.shard,features.shard-block-size,performance.low-prio-threads,cluster.data-self-heal-algorithm,cluster.locking-scheme,cluster.shd-wait-qlength,cluster.shd-max-threads,network.ping-timeout,user.cifs,performance.strict-o-direct,network.remote-dio,cluster.granular-entry-heal
value=virt,36,36,on,512MB,32,full,granular,10000,8,30,off,on,off,on
brick_dirs=/gluster/brick1/engine