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The Wednesday 2007-12-05 at 06:48 -0700, Bill Anderson wrote:
For perfomance, yes, you are right. For safety, no, you are wrong.
I don't see the safety issue as a major issue. The kernel avoids sending
dirty pages to swap. Also, any time the application does a write, the
dirty pages are sent to the buffer, and buffers aren't swapped. The
kernel does not swap any kernel data structure. Having mirrored swap
areas isn't going to protect buffers that kflushd hasn't sent to the
disk. In this case, my opinion is that performance takes precedence.
Performance takes precedence if the admin of that systems prefers
performance. If the admin prefers reliability (or needs), then reliability
takes precedence.
If the machine is to run 24*7, perhaps with hot-swappable disks, then
reliability takes precedence - and in that case swap *must* go on raid.
The trick is that with swap on raid, if one disk goes down the system
continues running till it is replaced with no impact on users or programs.
If you don't, then applications will simply stop (in iowait for ever) or
the kernel will panic. That means downtime! It is a major issue.
This difference is documented.
- --
Cheers,
Carlos E. R.
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