The storage.config file (by default, located in /usr/local/etc/trafficserver/) lists all the files, directories, and/or hard disk partitions that make up the Traffic Server cache. After you modify the storage.config file the new settings will not be effective until Traffic Server is restarted.


The format of the storage.config file is a series of lines of the form

pathname size [ volume=number ] [ id=string ]

where pathname is the name of a partition, directory or file, size is the size of the named partition, directory or file (in bytes), and volume is the volume number used in the files volume.config and hosting.config. id is used for seeding the Assignment Table. You must specify a size for directories; size is optional for files and raw partitions. volume and id are optional.


The volume option is independent of the id option and either can be used with or without the other, and their ordering on the line is irrelevant.


If the id option is used every use must have a unique value for string.


Any change to this files can (and almost always will) invalidate the existing cache in its entirety.

You can use any partition of any size. For best performance:

  • Use raw disk partitions.

  • For each disk, make all partitions the same size.

  • For each node, use the same number of partitions on all disks.

  • Group similar kinds of storage into different volumes. For example split out SSD’s or RAM drives into their own volume.

Specify pathnames according to your operating system requirements. See the following examples. In the storage.config file, a formatted or raw disk must be at least 128 MB.

When using raw disk or partitions, you should make sure the Traffic Server user used by the Traffic Server process has read and write privileges on the raw disk device or partition. One good practice is to make sure the device file is set with ‘g+rw’ and the Traffic Server user is in the group which owns the device file. However, some operating systems have stronger requirements - see the following examples for more information.

As with standard records.yaml integers, human readable prefixes are also supported. They include

  • K Kilobytes (1024 bytes)

  • M Megabytes (1024^2 or 1,048,576 bytes)

  • G Gigabytes (1024^3 or 1,073,741,824 bytes)

  • T Terabytes (1024^4 or 1,099,511,627,776 bytes)

Assignment Table

Each storage element defined in storage.config is divided in to stripes. The assignment table maps from an object URL to a specific stripe. The table is initialized based on a pseudo-random process which is seeded by hashing a string for each stripe. This string is composed of a base string, an offset (the start of the stripe on the storage element), and the length of the stripe. By default the path for the storage is used as the base string. This ensures that each stripe has a unique string for the assignment hash. This does make the assignment table very sensitive to the path for the storage elements and changing even one can have a cascading effect which will effectively clear most of the cache. This can be problem when drives fail and a system reboot causes the path names to change.

The id option can be used to create a fixed string that an administrator can use to keep the assignment table consistent by maintaining the mapping from physical device to base string even in the presence of hardware changes and failures.


The following basic example shows 128 MB of cache storage in the /big_dir directory:

/big_dir 134217728

You can use the . symbol for the current directory. Here is an example for 64 MB of cache storage in the current directory:

. 134217728

As an alternative, using the human readable prefixes, you can express a 64GB cache file with:

/really_big_dir 64G


When using on-filesystem cache disk storage, you can only have one such directory specified. This will be addressed in a future version.

Linux Example


Rather than refer to disk devices like /dev/sda, /dev/sdb, etc., modern Linux supports alternative symlinked names for disk devices in the /dev/disk directory structure. As noted for the Assignment Table the path used for the disk can effect the cache if it changes. This can be ameliorated in some cases by using one of the alternate paths in via /dev/disk. Note that if the by-id or by-path style is used, replacing a failed drive will cause that path to change because the new drive will have a different physical ID or path. The original hash string can be kept by adding id or path with the original path to the storage line.

If this is not sufficient then the id or path argument should be used to create a more permanent assignment table. An example would be:

/dev/sde id=cache.disk.0
/dev/sdg id=cache.disk.1

The following example will use an entire raw disk in the Linux operating system:

/dev/disk/by-id/[DiskA_ID]    volume=1
/dev/disk/by-path/[DiskB_Path]   volume=2

In order to make sure traffic_server will have access to this disk you can use udev(7) to persistently set the right permissions. The following rules are targeted for an Ubuntu system, and stored in /etc/udev/rules.d/51-cache-disk.rules:

# Assign DiskA and DiskB to the tserver group
# make the assignment final, no later changes allowed to the group!
SUBSYSTEM=="block", KERNEL=="sd[ef]", GROUP:="tserver"

In order to apply these settings, trigger a reload with udevadm(8)::

udevadm trigger --subsystem-match=block

FreeBSD Example

Starting with 5.1 FreeBSD dropped support for explicit raw devices. All devices on FreeBSD can be accessed raw now.

The following example will use an entire raw disk in the FreeBSD operating system:


In order to make sure traffic_server will have access to this disk you can use devfs(8) to persistently set the right permissions. The following rules are stored in devfs.conf(5):

# Assign /dev/ada1 and /dev/ada2 to the tserver user
own    ada[12]  tserver:tserver


Because relative paths in storage.config are relative to the base prefix, when using customized runroot it may be necessary to adjust such paths in storage.config or adjust runroot.yaml itself. Despite the name, the cachedir value is not used for this file.