squid-cache.org

# Uncomment and adjust the following to add a disk cache directory.
#cache_dir ufs /usr/local/squid/var/cache/squid 100 16 256

	Format:
		cache_dir Type Directory-Name Fs-specific-data [options]

	You can specify multiple cache_dir lines to spread the
	cache among different disk partitions.

	Type specifies the kind of storage system to use. Only "ufs"
	is built by default. To enable any of the other storage systems
	see the --enable-storeio configure option.

	'Directory' is a top-level directory where cache swap
	files will be stored.  If you want to use an entire disk
	for caching, this can be the mount-point directory.
	The directory must exist and be writable by the Squid
	process.  Squid will NOT create this directory for you.

	Rock is currently the only SMP-aware cache_dir type. Using other
	store types in configurations with multiple workers is not
	supported and may lead to HTTP violations or undefined behavior,
	even when each such cache_dir is given a dedicated worker using
	configuration conditionals.


	====  The ufs store type  ====

	"ufs" is the old well-known Squid storage format that has always
	been there.

	Usage:
		cache_dir ufs Directory-Name Mbytes L1 L2 [options]

	'Mbytes' is the amount of disk space (MB) to use under this
	directory.  The default is 100 MB.  Change this to suit your
	configuration.  Do NOT put the size of your disk drive here.
	Instead, if you want Squid to use the entire disk drive,
	subtract 20% and use that value.

	'L1' is the number of first-level subdirectories which
	will be created under the 'Directory'.  The default is 16.

	'L2' is the number of second-level subdirectories which
	will be created under each first-level directory.  The default
	is 256.


	====  The aufs store type  ====

	"aufs" uses the same storage format as "ufs", utilizing
	POSIX-threads to avoid blocking the main Squid process on
	disk-I/O. This was formerly known in Squid as async-io.

	Usage:
		cache_dir aufs Directory-Name Mbytes L1 L2 [options]

	see argument descriptions under ufs above


	====  The diskd store type  ====

	"diskd" uses the same storage format as "ufs", utilizing a
	separate process to avoid blocking the main Squid process on
	disk-I/O.

	Usage:
		cache_dir diskd Directory-Name Mbytes L1 L2 [options] [Q1=n] [Q2=n]

	see argument descriptions under ufs above

	Q1 specifies the number of unacknowledged I/O requests when Squid
	stops opening new files. If this many messages are in the queues,
	Squid won't open new files. Default is 64

	Q2 specifies the number of unacknowledged messages when Squid
	starts blocking.  If this many messages are in the queues,
	Squid blocks until it receives some replies. Default is 72

	When Q1 < Q2 (the default), the cache directory is optimized
	for lower response time at the expense of a decrease in hit
	ratio.  If Q1 > Q2, the cache directory is optimized for
	higher hit ratio at the expense of an increase in response
	time.


	====  The rock store type  ====

	Usage:
	    cache_dir rock Directory-Name Mbytes [options]

	The Rock Store type is a database-style storage. All cached
	entries are stored in a "database" file, using fixed-size slots.
	A single entry occupies one or more slots.

	If possible, Squid using Rock Store creates a dedicated kid
	process called "disker" to avoid blocking Squid worker(s) on disk
	I/O. One disker kid is created for each rock cache_dir.  Diskers
	are created only when Squid, running in daemon mode, has support
	for the IpcIo disk I/O module.

	swap-timeout=msec: Squid will not start writing a miss to or
	reading a hit from disk if it estimates that the swap operation
	will take more than the specified number of milliseconds. By
	default and when set to zero, disables the disk I/O time limit
	enforcement. Ignored when using blocking I/O module because
	blocking synchronous I/O does not allow Squid to estimate the
	expected swap wait time.

	max-swap-rate=swaps/sec: Artificially limits disk access using
	the specified I/O rate limit. Swap out requests that
	would cause the average I/O rate to exceed the limit are
	delayed. Individual swap in requests (i.e., hits or reads) are
	not delayed, but they do contribute to measured swap rate and
	since they are placed in the same FIFO queue as swap out
	requests, they may wait longer if max-swap-rate is smaller.
	This is necessary on file systems that buffer "too
	many" writes and then start blocking Squid and other processes
	while committing those writes to disk.  Usually used together
	with swap-timeout to avoid excessive delays and queue overflows
	when disk demand exceeds available disk "bandwidth". By default
	and when set to zero, disables the disk I/O rate limit
	enforcement. Currently supported by IpcIo module only.

	slot-size=bytes: The size of a database "record" used for
	storing cached responses. A cached response occupies at least
	one slot and all database I/O is done using individual slots so
	increasing this parameter leads to more disk space waste while
	decreasing it leads to more disk I/O overheads. Should be a
	multiple of your operating system I/O page size. Defaults to
	16KBytes. A housekeeping header is stored with each slot and
	smaller slot-sizes will be rejected. The header is smaller than
	100 bytes.


	==== COMMON OPTIONS ====

	no-store	no new objects should be stored to this cache_dir.

	min-size=n	the minimum object size in bytes this cache_dir
			will accept.  It's used to restrict a cache_dir
			to only store large objects (e.g. AUFS) while
			other stores are optimized for smaller objects
			(e.g. Rock).
			Defaults to 0.

	max-size=n	the maximum object size in bytes this cache_dir
			supports.
			The value in maximum_object_size directive sets
			the default unless more specific details are
			available (ie a small store capacity).

	Note: To make optimal use of the max-size limits you should order
	the cache_dir lines with the smallest max-size value first.

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