I'm looking for a layer 3 switch that has at least 24 ethernet ports and at least 2 SFP+ ports that can handle interface bonding and network address translation (also the smaller the form factor the better).

I currently have a MikroTik CRS226-24G-2S+IN but I don't think the CPU is going to be up to the task. 

What are my options here?

So you're looking for a 24 port router? Good luck with that.

Better buy a solid 24 port switch (like tp-link Jetstream or cisco sg300) and combine that with a router.

sounds more like top-notch CRS you need, especially if you expecting both 24 ports to be ~ more or less saturated most time.

I'm looking for a layer 3 switch that has at least 24 ethernet ports and at least 2 SFP+ ports that can handle interface bonding and network address translation (also the smaller the form factor the better).

I currently have a MikroTik CRS226-24G-2S+IN but I don't think the CPU is going to be up to the task. 

What are my options here?

keep in mind if you are looking for a SWITCH, a switch typically makes all the work using ASIC's because that the cpu of a switch is irrelevant because is mainly used to manage the switch.

In the case of mikrotik CRS switches only perform layer 2 functions by hardware using ASIC's, a especial and unique feature of CRS switches is they can use the CPU to work as a router, that can be a lot confusing because some people think can get layer 3 wire speed switching with a CRS, that's not the case., CRS switches CPU only can perform light layer 3 work, my advice: use CRS cpu only to manage the switch.

If you are looking for a layer 3 switch, there is a situation, each vendor implement different functions on layer 3 switches, you have to investigate user manual of the products to know what to expect of one or another vendor or model of layer 3 or layer 2 switch, reading manuals you can identify limitations on functionality of each specific switch, there is a lot of limitations on layer 3 switches, because there are based on ASIC's to get full wire-speed but these ACIS's have fixed functions on it, and this limitations are permanent until a new hardware revision of the product is released.
That's the reason of ROUTERS to exist, a router performs Layer 3 operations by software, because that a router can offer a lot of functionalities and can be improved or updated, because that  a router requires a lot of CPU power to emulate layer 3 performance of a layer 3 switch.

Another difference between a layer 3 switch and a router: the switch usually maintain its performance no matter what functionalities are you using, while routers do the opposite, a router performance is inversely proportional to the complexity of its configuration: more complex configuration = less performance

In your post i can see you are looking for equipment but your requirements are more related to interfaces and form factor

your requirement lack traffic sizing, thats the more important metric to define which equipment appropriate to this scenario.

i have some doubts:
you need 24 ethernet ports: why 24 ports?? fast ethernet ports? gigabit ethernet ports?? what kind and amount of traffic you need to pass across this interfaces??
you need bonding: why?? lacp?? to another router?? to another switch??
you need NAT: why?? is this a border router??

We would usually stick in a CRS switch, and plug it into e.g a CCR1009 (depending on the site) to handle any NAT, PPPoE etc... It is much cheaper than a proper layer 3 switch, e.g the cisco nexus series. We are also busy trialing some of the switches from edge-core (as they offer multiple SFP ports e.g >24) - however we would still only use it in a layer2 situation as an aggregation switch and pair it with a CCR. A new full layer3 switch is > $5k

you need 24 ethernet ports: why 24 ports?? fast ethernet ports? gigabit ethernet ports?? what kind and amount of traffic you need to pass across this interfaces??
you need bonding: why?? lacp?? to another router?? to another switch??
you need NAT: why?? is this a border router??

Thanks chechito, your post is very informative. To answer your questions:

• 24 ports because I will have up to 24 general-purpose Linux machines generating data each to a local disk (cache) before transferring to longer term storage system (over NFS).
• Gigabit ethernet ports
• LACP across 2 SPF+ ports to support data transfer from each of the 24 devices.
• NATing is required because the longer term storage won't be in the same ethernet.

Could the CCR1072-1G-8+S be used to do the NATing in conjunction with the CRS226-24G-2S+IN I already have? I'm guessing bonding (LACP) the SFP+ ports on the CRS226-24G-2S+IN would be a bad move for the reasons described in your post. What would be the recommend topology/configuration between the CCR and the CRS to achieve a 20Gbps link given the CCR limitations?

So, give up on LACP on the CRS...it doesn't exist.  CRS only supports static link aggregation (NOT 802.3ad compliant).  You can do 802.3ad at the CCR through bonding, but the CRS doesn't have enough CPU to support even 1 gbps of throughput over bonded ports.  Not sure how it would work if you had LACP on one side and only static link aggregation on the other...I wouldn't trust it for a production environment.

I have complained about this very thing a couple of time now.

For time being at the cheapest you're looking at something like TP-Link , Netgear M , Dell N series switches.

For crying out loud! There is no such thing as a small (cheap) switch with big performance.
It is some time since the CRS model are out, but most still don't get it that these are managed SWITCHES, not routers.

The ROS interface is there for management purposes, the low performance routing capabilities being a side effect of that.
Letting bonding aside (which is a big miss on the CRS), the moment you fiddle with IPs (like NAT), its a routing job, and the CRSs are not intended for that.
Get a router for that stuff, and if you need the advanced features get a CCR and use that as a switch, not the other way around.

Thanks for all your help, I now have a better understanding of the limitations of the CRS.

What would be the recommended topology for using the CRS226-24G-2S+IN (for switching) in conjunction with the CCR1072-1G-8+S (for NATing)?

• 24 ports because I will have up to 24 general-purpose Linux machines generating data each to a local disk (cache) before transferring to longer term storage system (over NFS).
• Gigabit ethernet ports
• LACP across 2 SPF+ ports to support data transfer from each of the 24 devices.
• NATing is required because the longer term storage won't be in the same ethernet.

Could the CCR1072-1G-8+S be used to do the NATing in conjunction with the CRS226-24G-2S+IN I already have? I'm guessing bonding (LACP) the SFP+ ports on the CRS226-24G-2S+IN would be a bad move for the reasons described in your post. What would be the recommend topology/configuration between the CCR and the CRS to achieve a 20Gbps link given the CCR limitations?

Why NAT? Just use a static route from the storage, to reach the machines. Can You do it? It would save a lot of CPU. Come to think of it: do You really need a router? I have no idea about the topology of your network. Wouldn't be easier to just stick a 24G + 2SFP+ switch? With VLANs You could do some traffic separation, if needed.

i offer you use SwitchChip then you can use full power your switch

I don't understand. You want a switch, but you want to use NAT? So you really want a router, not a switch? 

I don't have control over the host network hence I need (I think I need) NATing. I now understand (thanks to the members of this forum) that I need a router.

I am not a network engineer, the devices I have connected to my CRS226-24G-2S+IN are very small, in fact the whole unit including the switch is encased in a portable chassis. I want the ability to plug my device into any host network, receive a single address over DHCP and be able to offloaded data via NFS. As portability is a factor the size of the networking device(s) is something I was looking to minimise.

I am not a network engineer, the devices I have connected to my CRS226-24G-2S+IN are very small, in fact the whole unit including the switch is encased in a portable chassis. I want the ability to plug my device into any host network, receive a single address over DHCP and be able to offloaded data via NFS. As portability is a factor the size of the networking device(s) is something I was looking to minimise.

Well, in order to work this way You really need NAT. What, in turn, means You really need a router. This 24 clients of yours: do they speak to each other? Or just to the remote storage? If You don't need them to broadcast one another, there's no need to worry about bonding the two 10Gb interfaces. Just break the switch in two VLANs, each with half the Gb ports and one 10Gb.
Each 10Gb interface would connect to your router, and be a independent network. Let's say 10.x.0.0/24 and 10.y.0.0/24. The router would use bonding on the 2 WAN interfaces.
Just noticed: You said to have no control over the external network. Bonding is not a good idea, then. It needs support on both sides - and since You don't control the other LAN...
If You can live with just 10Gb, the setup is much easier.
1) Plug every client on the CRS.
2) Connect one 10Gb port of the CRS to one 10Gb port of the router. Forget about VLANs and whatnot.
3) Connect one 10Gb port of the router to the network of the storage. Done.
I can't speak about the NAT speed of the CCRs, so have no idea about which one You need. To use bonding, it would have to be the CCR1072-1G-8S+. Not much choice here, since it's the only one with 4 10Gb port available. By the way: the 10Gb ports are SFP, and they use fiber. Keep it in mind when planning the connection to your client.