Unfortunately if you have accidentally added a single drive into your raidz pool at the top-level there is no way to just remove the non redundant disk. Your pool is now dependant on this disk.
If you want your pool to be just raidz vdevs, then you will need to backup your data, destroy your pool, create a new pool, and restore your data.
There is no current way to remove a top-level vdev from a pool.
The first place to look for increasing your hit ratio is the refresh_pattern parameter within the squid.conf file.
Note: the following applies to squid 3.0 and higher only….
I have found a really good page here http://linux.com/archive/feature/153221 that explains some good setups if you with to increase your cache hits…
refresh_pattern ^ftp: 1440 20% 10080
refresh_pattern ^gopher: 1440 0% 1440
refresh_pattern -i \.(gif|png|jpg|jpeg|ico)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private
refresh_pattern -i \.(iso|avi|wav|mp3|mp4|mpeg|swf|flv|x-flv)$ 43200 90% 432000 override-expire ignore-no-cache ignore-no-store ignore-private
refresh_pattern -i \.(deb|rpm|exe|zip|tar|tgz|ram|rar|bin|ppt|doc|tiff)$ 10080 90% 43200 override-expire ignore-no-cache ignore-no-store ignore-private
refresh_pattern -i \.index.(html|htm)$ 0 40% 10080
refresh_pattern -i \.(html|htm|css|js)$ 1440 40% 40320
refresh_pattern . 0 40% 40320
This is an example of a site that you may wish to heavily cache…
refresh_pattern -i youtube.com/.* 10080 90% 43200
# REMOVE these lines from squid.conf
acl QUERY urlpath_regex cgi-bin \?
cache deny QUERY
# Break HTTP standard for flash videos. Keep them in cache even if asked not to.
refresh_pattern -i \.flv$ 10080 90% 999999 ignore-no-cache override-expire ignore-private
# Apparently youtube.com use 'Range' requests
# - not seen, but presumably when a video is stopped for a long while then resumed, (or fast-forwarded).
# - convert range requests into a full-file request, so squid can cache it
# NP: BUT slows down their _first_ load time.
quick_abort_min -1 KB
# Also videos are LARGE; make sure you aren't killing them as 'too big to save'
# - squid defaults to 4MB, which is too small for videos and even some sound files
maximum_object_size 4 GB
# Let the clients favorite video site through with full caching
# - they can come from any of a number of youtube.com subdomains.
# - this is NOT ideal, the 'merging' of identical content is really needed here
acl youtube dstdomain .youtube.com
cache allow youtube
# kept to demonstrate that the refresh_patterns involved above go before this.
# You may be missing the CGI pattern, it will need to be added if so.
refresh_pattern -i (/cgi-bin/|\?) 0 0% 0
refresh_pattern . 0 0% 4320