You can perform normal or selective dumps on systems with any amount of memory, including those with more than 4GB of memory. In a normal dump, all physical memory is dumped to disk. There are two types of selective dump: a selective dump that dumps only kernel mapped memory (default), or a more abbreviated selective dump that dumps only a portion of kernel mapped memory. The system dump memory image can be examined using crash(ADM).
If you have experienced a system panic the relevant information for diagnosis is usually in the kernel pages. On a system with large memory, it can be more practical to perform a selective dump. This means that the dump is quicker and smaller at the expense of some information (user space pages). A selective dump is made at the time of the panic, but you must specify that you want a selective dump when the system is booted. Set the kernel tunable parameter SYSDUMP_SELECTIVE to ``1'' to obtain a selective dump for kernel mapped memory, or set it to ``2'' for an abbreviated, selective dump.
You might want to specify a selective dump if your system has a large amount of physical memory or if maximum use of disk space is required (keeping the swap/dump slice as small as possible to free up disk for filesystems).
If a system dump is directed to a dump device other than the default swap device, the dump will not be detected when the system boots up. To enable the system to detect a dump that is not in the swap area when the system boots, add the following entry into the file /etc/dumptab:
/dev/dump 0 -
Use the following information to configure the swap/dump space for best results for the amount of memory on your system:
dump_space >= physical_memory_size/2
dump_space >= 128MB + SEGKMEM_PSE_BYTES + (general_memory_size - 256MB)/4where general_memory_size is the output of memsize -g.
For example: a system with 64MB of physical memory should have 32MB dump space; a system with 512MB of physical memory should have 192MB dump space; and, a system with 1GB of physical memory should have 320MB dump space.
Dump space should never be sized larger than 1.5GB for selective dumps, but can be larger for full dumps.