What is the Best OS for Squid?

This is an all-time favourite FAQ, bound to show up every month or so on the Squid Users mailing-list.

Generally speaking, any modern Unix or Unix-like operating system will offer similarly good performance. A technically sensible administrator will choose the best tool for the job, which means whatever OS she is most comfortable with.

For reference we maintain an incomplete list of OS where Squid is known to be popular. Where possible there are also OS pages here in the wiki with extra information.

Popular OS

Tuning for More

What matters the most to obtain the most out of any setup is to properly tune a few parameters. In priority order:

• amount of physical memory available
  • the more the better, squid performance will suffer badly if parts of it are swapped out of core memory
• CPU speed and core count
  • few faster cores are better than many slow cores. SMP Squid can currently operate most efficiently with 4-8 cores of 3GHz or more. multi-tenant installations are better for machinery with very many cores.
  • only the physical cores are useful, hyper-threaded "cores" can actually be worse.
• Number of harddrives used for cache and their architecture

  • squid disk access patterns hit particularly hard RAID systems - especially RAID4/5. Since the data are not by definition valuable, it is recommended to run the cache_dirs on JBOD ¹ (see SquidFaq/RAID)

  • of course the disk type matters: SCSI performs better than ATA, 15kRPM is better than 5.4kRPM, etc.
• noatime mount option
  • atime is just useless for cache data - squid does its own timestamping, mounting the filesystem with the noatime option just saves a whole lot of writes to the disks
• amount of space used
  • always leave about 20% of free space on the filesystems containing your cache_dirs: generally FS performance degrades dramatically if used space exceeds 80%
• type of filesystem
  • only applies on OSes which offer multiple choices (except for a few really bad choices of FS). see below.

On systems with synchronous directory updates (Solaris, some BSD versions)

• mount option to enable asynchronous directory updates, or preferably a filesystem meta journal on a separate device taking the heat of directory updates.