现在服务器内存配置越来越大，以往比较通用的Memory * 1.5的原则基本不再适用，下面是网上收集来的新的分配原则，基于Red Hat Linux的建议，也适合其它Unix。
1）安装系统时难以确定内存的负荷，如何设置交换分区大小
2）系统中物理内存越大，所需交换分区就会越少
因此，在Red Hat Enterprise Linux 5中，以下是设置合适的交换分区大小的规则：
小于等于4G物理内存的系统，至少设置2GB的交换分区
4G～16G物理内存的系统，至少设置4GB的交换分区
16G～64G物理内存的系统，至少设置8GB的交换分区
64G～256G物理内存的系统，至少设置16GB的交换分区
There is no fixed rule to size swap. It depends on the application requirement. The rule of thumb I use is:
ifRAM<4GB: swap=2xRAM if RAM is between 4GB - 8GB, swap=RAM if RAM>8GB swap=8GB
The best way is to reserve some disk space for future growth in case you need more swap space and monitor the system.
/var sizing is not related to the physical memory. /var is used to store log, temporary files, spool and core dumps. For example, if the machine is used as mail or print server and it has a lots of messages or print jobs, you need to size /var bigger. Also, when machine crashes, if savecore is enabled, the OS will automatically try to save the kernel dump to /var/crash directory. 10G is kind of overkill but it doesn't hurt as long as you have enough space.
