Forum OpenACS Development: Re: File Storage Archive download locks up the server
What resource is the zip command using up? CPU, disk, memory? Does running a zip command manually at the command line have the same effect? Some tools to help you figure that out: dstat, iostat (part of the sysstat package in Debian/Ubuntu), top, vmstat, mpstat.
My wild guess is that your zip command is tying up your disk I/O rather than your cpu, as in my experience, that is more likely to cause obvious system-wide lag.