We are planning to move mysql to dedicated box. At this moment we have web servers and mysql is running on each. Question is: cheaper is to buy 10G switch and put 10G network card into mysql server. Or buy normal gigabit switch and connect mysql box to switch with multiple network cables. In 1G scenario then we give each web server different mysql IP address. I don't think, that mysql box with one 1G link is enough to to satisfy multiple web box mysql traffic.
At this moment we have 3 servers witch are running mysql/web. Plan is to add fourth server for mysql only. Thanks.
Edit:
if we buy 1G switch with mini-GBIC ports. Can we put in mini-GBIC 10G connectors and then connect mysql box to that port?
SQL is inherently quite a bandwidth-light system, unless you're doing a LOT of big bulk loads or routinely need to pull down massive results you won't see much benefit from using 10Gbps NICs. There IS one area where it can be useful, if you backup over Ethernet and have sufficient data to justify the cost.
What I'd do is monitor your network traffic at 1Gbps and if you see consistent, prolonged NIC use at >95% of 1Gbps then consider the 10Gbps option, otherwise stick with 1Gbps for now.
You can use generic load balancing bonding or with LACP (switch must support it). Total bandwidth can reach the sum of all physical connections (4 gb for four 1 gb links to the MySQL server), but bandwidth for single connection will be limited to single link (1 gb). I definitely recommend to use LACP to eliminate TCP re-transmissions.