Hello,

I am creating LAN where there will be about 70 sockets,
I will want to connect couple switches together with router and synology nas in such manner,

RB5009UPr+S+IN First PORT SFP+ > to First PORT SFP+ on CRS326-24G-2S+RM Second PORT SFP+ to > First PORT SFP+ on CRS326-24G-2S+RM Second PORT SFP+ to > First PORT SFP+ on CRS326-24G-2S+RM and Second PORT SFP+ to > S+RJ10 Module > finally to Synology NAS 10G RJ45

On each CRS326-24G-2S+RM, there will be connected about 23pcs of rj45 cables to destination sockets.

Disable all functionality such as VLAN, MAC Mapping, Port redirection ect on all CRS326-24G-2S+RM
And Setup all that on router.
Router connected to isp by 2.5G ethernet port
Is it possible to do so ?

Yes. And the beauty ? On CRS326 you do not have to do anything except for changing IP address.

Thanks, downside of that solution is, when any switch goes down, whole network will break?.

That's a logical consequence from daisy-chaining those switches one after the other.

Only the part which is behind the switch which breaks down, will go down.
If it's the first one, everything goes down.
If it's the last one, only 24 clients will go down.

If it's the RB5009 going down, everything is down too. Also thought of that ?

That's something you need to consider and take into account.
Do you accept a single point of failure or not ?
Same with a stupid power supply. Only one or multiple ?
Keep spare power supply next to device (and TEST it works !) or use devices with multiple power supplies (they exist) ?
UPS for power or not ?
Fall-back network paths or not ?

A lot is possible to absorb problems but cost will go up as well depending on how it is implemented.
I'm not really into that segment but I am aware things can go wrong.

Good point, for now i will have to stick to no reduntant PSU, if there is need and something happens "Client" will invest i guess.

Do you have any informations that RB5009UPr+S+IN can be tricky when using 2.5Gbit port for ISP and transfer goes above 1Gbit and also SPF+ i utilized to connect to CRS326-24G-2S+RM SPF+,
I have read that there are some problems that router can make lags or some kind of problems?.
I also wonder if that router will be okay considering it will have around 80 clients under it.

Do you have any informations that RB5009UPr+S+IN can be tricky when using 2.5Gbit port for ISP and transfer goes above 1Gbit and also SPF+ i utilized to connect to CRS326-24G-2S+RM SPF+,
I have read that there are some problems that router can make lags or some kind of problems?.

Not that I am aware of (at least not on the devices I have).
If it was so the forum would be swamped with reports saying so.

All 8 ether ports including that SFP+ port are connected to one single Marvel switch chip.
If configured in a normal way, there will be no lags.
(tip: 1 bridge is enough for most applications. Don't start playing with multiple bridges if there is no good reason to do so or you will break HW offload and then traffic needs to pass CPU which might impact performance)

I also wonder if that router will be okay considering it will have around 80 clients under it.

It will most likely not even sweat
Obviously, it all depends what other functions you will add to that device and how you use your firewall.

Good point, for now i will have to stick to no reduntant PSU, if there is need and something happens "Client" will invest i guess.

The CRS326 can be powered by passive PoE too. If You want redundancy of power, use the PSU included, and a PoE injector.
By the way: so does the RB5009. I used to do this with one of them too.

RB5009 even has a 3th powering option on the side.

Also, POE version of RB5009 can be powered using POE on ALL 8 ether ports.

Also, POE version of RB5009 can be powered using POE on ALL 8 ether ports.

There are two RB5009 models. One can be powered on all ports, the other only ether1.