Any ideas for making an OpenBSD usable (how to turn off logs, "put os into memory"?) on a SDHC or an microSDHC card? Since full-disk encryption is not really a solution under OpenBSD so I though I would be more keen on physical protection, so I will install/use my "desktop os" on an SDHC or a microSDHC card.
The generally accepted practice for installing onto a flash device is the same as installing onto any other disk. The entire OpenBSD base system will readily fit in 1GB of space. It will likely be harder to find a flash device that small than to get OpenBSD installed on it.
As far as turning off logging, don't worry about it, just let them be written to your flash card, it is not likely to kill the card. Alternatively, send your logs to a remote host, or mount /var onto a different filesystem.
Also, when you boot, the OS is loaded into memory for you... no extra tweaking required.
There are official FAQ's on this.
Also, on the topic of boot disk encryption, a recent article on undeadly points out that it is possible; though, I would imagine, at the moment that procedure is not officially supported by OpenBSD.
You are running OpenBSD as you're Desktop OS and you seem to have to deal with the fact that your IO isn't safe from prying eyes ? Well there Neo ;) ... I would suggest...
A simple cardreader, it's a scsi device in the end.
Get a Sandisk HD Video SDHC 32GB Class 6 card to make the 20Mb/s & don't forget the softdeps in the fstat