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See the License for the specific language governing permissions and limitations under the License. .. include:: ../../common.defs ============== storage.yaml ============== .. configfile:: storage.yaml The :file:`storage.yaml` 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 :file:`storage.yaml` file the new settings will not be effective until Traffic Server is restarted. Format ====== The format of the :file:`storage.yaml` file is a series of lines of the form .. code-block:: yaml cache: # file level key spans: # - name: # name of the span path: # path to storage size: # size in bytes, required for file system storage, optional for raw device hash_seed: # optional, used to isolate lookup from path changes volumes: # optional - id: # identifier [1-255] size: # optional, size in bytes or percentage scheme: # optional, default to "http" ram_cache: # optional, default to "true" avg_obj_size: # optional, overrides proxy.config.cache.min_average_object_size fragment_size: # optional, overrides proxy.config.cache.target_fragment_size spans: # optional - use: # Span identifier size: # size allocated to this volume :code:`spans` lists the raw storage used for the cache. :code:`volumes` organizes the storage into locations for storing cached objects. This is very similar to operating system partitions and file systems. For :code:`spans` the keys are +---------------+-------------+-------------------------------------------------------------+ | Key | Type | Meaning | +===============+=============+=============================================================+ | name | string | Name of the span. | +---------------+-------------+-------------------------------------------------------------+ | path | string | File system of the storage. This must be a block device or | | | | directory. | +---------------+-------------+-------------------------------------------------------------+ | size | bytes | Size in bytes. This is optional for devices but required | | | | for directories. | +---------------+-------------+-------------------------------------------------------------+ | hash_seed | string | Hashing for object location uses a seed to randomize the | | | | hash. By default this is the path for the span. | +---------------+-------------+-------------------------------------------------------------+ For :code:`volumes` the keys are +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | Key | Type | Meaning | +==================+=============+=========================================================================================================+ | id | integer | Id of the volume. Range is [1-255]. This id can be referred | | | | from :file:`hosting.config`. Each volume must have a distinct id; volume number 0 is reserved | | | | for internal use. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | size | bytes | Target size of the entire volume. This can be an absolute | | | _or_ | number of bytes or a percentage. | | | percentage | | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | scheme | enumeration | Protocol scheme, defaults to "http". Preserved for future | | | string | use. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | ram_cache | boolean | Control of ram caching for this volume. Default is ``true``. This may be desirable if you are using | | | | something like ramdisks, to avoid wasting RAM and CPU time on double caching objects. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | ram_cache_size | bytes | Allocate a dedicated RAM cache pool for this volume. | | | | The specified amount is automatically subtracted from the global RAM cache pool; the remainder is | | | | shared among volumes without a private allocation. Setting to ``0`` disables the RAM cache for this | | | | volume (equivalent to ``ram_cache: false``). If the sum of all per-volume allocations exceeds the | | | | global limit, Traffic Server will fail to start with a fatal error. If ``ram_cache: false`` is also | | | | set, this value is ignored with a warning. Only takes effect when the global size is a positive value | | | | (not ``-1`` for automatic sizing). | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | ram_cache_cutoff | bytes | Overrides the global :ts:cv:`proxy.config.cache.ram_cache_cutoff` configuration for this volume. | | | | Objects larger than this size will not be placed in the RAM cache for this volume. Use a larger | | | | cutoff for volumes serving frequently accessed large objects, a smaller cutoff for volumes with many | | | | small objects to maximize RAM cache hits, or a very low cutoff to effectively disable RAM caching for | | | | large objects on that volume. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | avg_obj_size | integer | Overrides the global :ts:cv:`proxy.config.cache.min_average_object_size` configuration for this volume. | | | | This is useful if you have a volume that is dedicated for say very small objects, and you need a lot of | | | | directory entries to store them. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | fragment_size | integer | Overrides the global :ts:cv:`proxy.config.cache.target_fragment_size` configuration for this volume. | | | | This allows for a smaller, or larger, fragment size for a particular volume. This may be useful | | | | together with ``avg_obj_size`` as well, since a larger fragment size could reduce the number of | | | | directory entries needed for a large object. Note that this setting has a maximmum value of 4MB. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ | spans | list | Spans that provide storage for this volume. Defaults to | | | | all spans. | +------------------+-------------+---------------------------------------------------------------------------------------------------------+ For :code:`volumes:spans` the keys are +---------------+-------------+-------------------------------------------------------------+ | Key | Type | Meaning | +===============+=============+=============================================================+ | use | string | Name of the span to use. | +---------------+-------------+-------------------------------------------------------------+ | size | bytes | Amount of the span to use. The total across all uses of | | | _or_ | this specific span must be less than 100% and less than the | | | percentage | total size of the span. | +---------------+-------------+-------------------------------------------------------------+ Each volume is striped across several disks to achieve parallel I/O. For example: if there are four disks, then a 1-GB volume will have 256 MB on each disk (assuming each disk has enough free space available). If you do not allocate all the disk space in the cache, then the extra disk space is not used. You can use the extra space later to create new volumes without deleting and clearing the existing volumes. .. important:: Any change to this file 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. - 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 :file:`storage.yaml` file, a formatted or raw disk must be at least 128 MB. When using raw disk or partitions, you should make sure the :ts:cv:`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) Storage Allocation ------------------ Allocation of span storage to volumes is done in stages. Storage is always allocated in multiples of 128 megabytes, rounded down. * Explicitly sized span storage (:code:`cache:volumes:spans:size`) is allocated to volumes. It is an error if the total allocated is larger than the span size. * Absolute sizes are allocated first. * Percentages are allocated from remaining space. * Remaining storage from spans that are used without an explicit size is divided evenly among the volumes that use the span. * Span storage is allocated to volumes by the :code:`cache:volumes:size` values. * Absolute sizes are allocated first. * Percentages are applied to remaining space. * Remaining storage is divided evenly among volumes without an explicit size. .. _storage-assignment-table: Assignment Table ---------------- Each storage element defined in :file:`storage.yaml` is divided into :term:`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 a problem when drives fail and a system reboot causes the path names to change. The :arg:`name` 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. Backwards Compatibility ----------------------- In previous versions of |TS| it was possible to have "exclusive" spans which were used by only one volume. This is now done by specifying the span in the volume and using a size of "100%". .. important:: In the old volume.config, absolute sizes were specified in **megabytes** (e.g., ``size=512`` meant 512 MB). In :file:`storage.yaml`, sizes are specified in **bytes** with optional human-readable suffixes (e.g., ``size: 512M`` or ``size: 536870912``). A bare number without a suffix is interpreted as bytes, not megabytes. E.g. old configuration like :: /dev/disk2 volume=3 # storage.config volume=3 scheme=http size=512 # volume.config The corresponding configuration would be .. code-block:: yaml cache: spans: - name: disk.2 path: /dev/disk2 volumes: - id: 3 spans: - use: disk.2 size: 512M Because volume sizes that are percentages are computed on span storage not already explicitly allocated, this will leave none of "disk.2" for such allocation and therefore "disk.2" will be used only by volume "1". Note this configuration is more flexible. If it was useful to have two linear volumes, each using exclusively half of the span, this would be .. code-block:: yaml cache: spans: - name: disk.2 path: /dev/disk2 volumes: - id: 1 spans: - use: disk.2 size: 50% - id: 2 spans: - use: disk.2 size: 50% .. important:: If a span is explicitly used by any volume its storage will be allocated to only volumes that explicitly use that span. Examples ======== The following basic example shows 128 MB of cache storage in the "/big_dir" directory .. code-block:: yaml cache: spans: - name: store path: /big_dir size: 134217728 As an alternative, using the human readable prefixes, you can express a 64GB cache file with .. code-block:: yaml cache: spans: - name: store path: /really_big_dir size: 64G By default a volume uses all spans, therefore a volume uses all of span "store" because there are no other volumes. It would be equivalent to using the spans explicitly, e.g. .. code-block:: yaml cache: spans: - name: store path: /big_dir size: 128M volumes: - id: 1 size: 100% spans: - use: store You can use the ``.`` symbol for the current directory. Here is an example for 128 MB of cache storage in the current directory .. code-block:: yaml cache: spans: - name: store path: "." size: 128M .. note:: 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 ------------- .. note:: 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 :ref:`storage-assignment-table` the path used for the disk can affect 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. If this is not sufficient then the :arg:`hash_seed` key should be used to create a more permanent assignment table. An example would be .. code-block:: yaml cache: spans: - name: "span.0" path: "/dev/sde" hash_seed: "cache.disk.0" - name: "span.1" path: "/dev/sdg" hash_seed: "cache.disk.1" The following example will use an entire raw disk in the Linux operating system .. code-block:: yaml cache: spans: - name: a path: "/dev/disk/by-id/disk-A-id" - name: b path: "/dev/disk/by-id/disk-B-id" volumes: - id: 1 spans: - use: a size: 100% - id: 2 spans: - use: b size: 100% In order to make sure :program:`traffic_server` will have access to this disk you can use :manpage:`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 :manpage:`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 .. code-block:: yaml cache: spans: - name: ada.1 path: "/dev/ada1" - name: ada.2 path: "/dev/ada2" volumes: - id: 1 size: 100% In order to make sure :program:`traffic_server` will have access to this disk you can use :manpage:`devfs(8)` to persistently set the right permissions. The following rules are stored in :manpage:`devfs.conf(5)`:: # Assign /dev/ada1 and /dev/ada2 to the tserver user own ada[12] tserver:tserver Advanced -------- Because relative paths in :file:`storage.yaml` are relative to the base prefix, when using customized runroot it may be necessary to adjust such paths in :file:`storage.yaml` or adjust ``runroot.yaml`` itself. Despite the name, the cachedir value is not used for this file. Examples ======== The following example partitions the cache across 5 volumes to decrease single-lock pressure for a machine with few drives. The last volume being an example of one that might be composed of purely ramdisks so that the ram cache has been disabled. .. code-block:: yaml cache: spans: - name: disk path: "/dev/sdb" volumes: - id: 1 size: 20% - id: 2 size: 20% - id: 3 size: 20% - id: 4 size: 20% avg_obj_size: 4096 - id: 5 size: 20% ram_cache: false This can be simplified by depending on the default allocation which splits unallocated span storage across volumes. .. code-block:: yaml cache: spans: - name: disk path: "/dev/sdb" volumes: - id: 1 - id: 2 - id: 3 - id: 4 - id: 5 ram_cache: false For a host with a physical disk and two ram disks, where the ram disks should be split between two volumes, with a third volume that uses the physical disk. This depends on defaults. The spans "ram.1" and "ram.2" are split evenly between volume "1" and volume "2" because no sizes are specified. Span "disk" is not used for volume "1" nor volume "2" because it is not listed in the ``spans``. Volume "3" therefore gets all of span "disk". .. code-block:: yaml cache: spans: - name: disk path: "/dev/sdb" - name: ram.1 path: "/dev/ram.1" - name: ram.2 path: "/dev/ram.2" volumes: - id: 1 spans: - use: ram.1 - use: ram.2 - id: 2 spans: - use: ram.1 - use: ram.2 - id: 3 If one of the ram disk based volumes should be larger, this could be done as follows by making volume "1" roughly twice as large as volume "2". .. code-block:: yaml cache: spans: - name: disk path: "/dev/sdb" - name: ram.1 path: "/dev/ram.1" - name: ram.2 path: "/dev/ram.2" volumes: - id: 1 spans: - use: ram.1 size: 66% - use: ram.2 size: 66% - id: 2 spans: - use: ram.1 - use: ram.2 - id: 3 Instead, suppose the physical spans ("disk.1" and "disk.2") should be split across volumes. This can be done by adding volumes with only defaults, as the physical spans will be divided evenly among four volumes (3 - 6), each volume allocated 25% of "disk.1" and 25% of "disk.2". OTOH, the ram spans ("ram.1" and "ram.2") will be divided evenly among volume 1 and 2. .. code-block:: yaml cache: spans: - name: disk.1 path: "/dev/sdb" - name: disk.2 path: "/dev/sde" - name: ram.1 path: "/dev/ram.1" - name: ram.2 path: "/dev/ram.2" volumes: - id: 1 spans: - use: ram.1 - use: ram.2 - id: 2 spans: - use: ram.1 - use: ram.2 - id: 3 - id: 4 - id: 5 - id: 6 The following example shows advanced RAM cache configuration with dedicated allocations and custom cutoffs. Assuming a global :ts:cv:`proxy.config.cache.ram_cache.size` of 4GB, volume 1 receives a dedicated 2GB RAM cache pool, volume 2 gets 512MB and only caches objects up to 64KB, and volume 3 shares the remaining 1.5GB (4GB - 2GB - 512MB) and caches objects up to 1MB. .. code-block:: yaml cache: spans: - name: disk path: "/dev/sdb" volumes: - id: 1 size: 40% ram_cache_size: 2G - id: 2 size: 20% ram_cache_size: 512M ram_cache_cutoff: 64K - id: 3 size: 40% ram_cache_cutoff: 1M