[GRLUG] Solid State Drives

[Collin Kidder]

Adam Tauno Williams wrote:
>
>  I have a server with 8Gb of RAM and 8Gb of SWAP and an average of
> something like 60% swap used - the performance is great.  I've got 4Gb
> in my laptop and usually have ~100MB in the swap (sometimes it surges
> upward) - performance is good.  I don't think measuring utilization of
> swap is a meaningful performance benchmark at all;  paging is what is
> bad.  To know your paging rate you need to watch something like dstat;
> a tiny bit of swap with allot of paging is bad,   a large amount of used
> swap with essentially no paging is just fine (possibly even good). 
>   
I still contend that swap space is good for nothing more than a safety 
net. If you are using 60% of an 8GB swap space then why not just load 
that nearly never used data from disk when you need it? After all, you 
are effectively doing that anyhow. Virtualized memory brings many 
advantages but swap space isn't one of the better ones. It's vastly 
overrated.

You do NOT want to use a 30MB/s hard drive to supplement the storage 
space of a 6GB/s interface. It makes no sense. Back in the old days 
(like in the Windows 3.1 days) it made some sense. RAM was maybe 300MB/s 
and the harddrive 5MB/s. That's a 60:1 ratio. RAM was very expensive and 
people didn't run too many concurrent apps anyway. Nowdays the 6GB/30MB 
ratio is 200:1 so swapping is much more costly. Add in the bigger sizes 
these days (in the Windows 3.1 era your swap space might have been 
256MB, now it could be 4GB or more) and the problem is exasperated. Swap 
is a dead end. If you are using it then one of two things has occurred: 
1. You didn't buy enough RAM 2: You loaded more crap into your virtual 
memory than you needed to.