ZSD has been using Debian since 1997. We are an Internet Service Provider and we specialize in setting up and supporting on-site servers for small to medium based clients. We provide remote and telephonic support for these servers, our clients often have no Linux specific skills. These servers provide firewalls (shorewall), dns (bind, power-dns), dhcp (isc-dhcp), e-mail (exim, dovecot, roundcube), anti-virus/anti-spam (clamav, spamassassin), vpn's (openvpn, racoon), proxies (squid, dansgaurdian, sarg), webservices (apache, php, mysql), backups (rdiff-backup), raid storage (Linux RAID1 software) and file services (samba). We use Debian on our 14 in house servers and we have nearly 200 Debian servers under maintenance contracts on client premises.
Debian servers are very stable and they facilitate easy software upgrades, including major upgrades, over remote links. Linux RAID software allows for flexible hardware upgrades and easy recovery from hardware failures without excessive downtime and no Linux specific skills on site.