table of contents
| AMANDA-DEVICES(7) | Miscellanea | AMANDA-DEVICES(7) |
NAME¶
amanda-devices - Configuring and Using Amanda Devices
DESCRIPTION¶
The Device API specifies a generic interface between Amanda and storage devices such as tapes or disks. This manual page describes the device drivers included with Amanda.
This is a user-level description of the API, and does not address details that are only of concern to developers. For that purpose, consult the Amanda source code and http://wiki.zmanda.com.
The term "device driver" describes the software that can communicate with some kind of backend storage, e.g., a tape driver. A "device" is the storage element itself, usually a piece of hardware. When discussing a device and its driver as a unit, the term "device" is sometimes also used to refer to the combination of device and driver.
SPECIFYING DEVICES¶
Device names take the form TYPE:NODE, where TYPE selects a device driver, and NODE provides further information to that driver. The syntax for each device driver is given in the corresponding section below.
Devices are described in amanda.conf(5) with "device" sections, e.g.,
define device top_drive {
tapedev "tape:/dev/nst0"
device_property "BLOCK_SIZE" "131072"
}
A device defininition creates a device "alias", in this case named
top_drive, which can then be named in the global tapedev
parameter:
tapedev "top_drive"
The global tapedev parameter can also specify a literal device name. For example,
tapedev "file:/amdisks"is equivalent to
tapedev "default"
define device default {
tapedev "file:/amdisks"
}
Device properties specified outside of any device definition apply to all
devices. This syntax is provided mainly for backward compatibility, and for
simple Amanda configurations. Note that there is no way to provide properties
specific to a device without defining a device alias.
See amanda.conf(5) for more information on Amanda configuration.
DEVICES¶
This section lists the device drivers included with Amanda, and basic instructions for using them. For complete How-To information, consult the Amanda wiki at http://wiki.zmanda.com.
Null Device¶
tapedev "null:"
The null device driver only supports writing, and discards all data. It is generally only useful for testing purposes.
RAIT Device¶
tapedev "rait:tape:/dev/rmt/tps0d{4,5,6}n"
The RAIT device driver mirrors or stripes data over multiple "child" devices. The child devices are specified using a shell-like syntax, where alternatives are enclosed in braces and separated by commas.
With two child devices, the RAIT device driver mirrors data such that the two devices contain identical data and can be used singly for recovery. With more than two devices, the RAIT device "stripes" data across all but one device and writes a parity block to the final device, usable for data recovery in the event of a device or volume failure. The RAIT device scales its blocksize as necessary to match the number of children that will be used to store data.
When a child device is known to have failed, the RAIT device should be reconfigured to replace that device with the text "ERROR", e.g.,
tapedev "rait:{tape:/dev/st0,ERROR,tape:/dev/st2}"
This will cause the RAIT device to start up in degraded mode, reconstructing the
data from the missing device.
Like ordinary RAID drivers, the RAIT device driver can automatically enter degraded mode when one of its child devices fails. However, the RAIT device cannot automatically recover from any write error nor write any data in degraded mode. When reading, certain errors may be fatal (rather than causing degraded mode). And in any case, labels on all volumes must initially match (labeled or otherwise). If you have lost one volume from a set, explicitly start the device in degraded mode as described above.
Child Device Block Sizes¶
The RAIT device driver requires that all of its child devices use the same block size. If no block sizes are specified, the driver selects the block size closest to 32k that is within the MIN_BLOCK_SIZE - MAX_BLOCK_SIZE range of all child devices, and calculates its own blocksize according to the formula rait_blocksize = child_blocksize * (num_children - 1). If a block size is specified for the RAIT device, then it calculates its child block sizes according to the formula child_blocksize = rait_blocksize / (num_children - 1). Either way, it sets the BLOCK_SIZE property of each child device accordingly.
S3 Device¶
tapedev "s3:foocorp-backups/DailySet1-" device_property "S3_ACCESS_KEY" "MYACCESSKEY" device_property "S3_SECRET_KEY" "MYSECRETKEY"
The S3 device driver uploads data to the Amazon S3 "storage cloud". Its device name is a slash-sparated combination of bucket name and prefix: "s3:BUCKET/PREFIX". Since buckets must be unique across all Amazon S3 users, and since the number of buckets allowed to each user is limited, the driver can store multiple Amanda volumes in a single S3 bucket, distinguished by prefix. The prefix and slash can be omitted if they are not needed: "s3:BUCKET".
The access and secret keys used to authenticate to Amazon S3 are provided as properties.
The S3 device driver stores each block in a distinct S3 object. Due to high HTTP overhead for each request, use of larger than normal block sizes (> 1 megabyte) is reccomended with the S3 device.
You can control where your data is physically stored by Amazon S3 using a location constraint. Setting this affects can affect both billing and legal concerns, so you are encouraged to consult Amazon´s documentation for details.
To control location constraints, set the S3_BUCKET_LOCATION property. Currently, there are two valid settings: "" (any location) and "EU" (Europe). If the S3_BUCKET_LOCATION is set, Amanda will check to make sure that the setting agrees with the constraint currently on the bucket.
Tape Device¶
tapedev "tape:/dev/nst0"
The tape device driver interacts with a tape drive. The device uses the operating system´s built-in tape support, which is generally similar to that available via the command-line utilities dd(1) and mt(1).
The tape device name should specify a path to the operating system´s device file.
VFS Device¶
tapedev "file:/path/to/vtape"
The VFS device driver stores data on a UNIX filesystem. Note that although one typically uses the VFS device driver to store data on hard disks, the driver does not interface with any hardware on a block level.
The device name specifies a path to a directory which must exist and contain a "data/" subdirectory. Each tape file is stored as a distinct file in this directory, the name of which reflects the Amanda header in the tape file. Block boundaries are not maintained: the driver supports reads of arbitrary size, regardless of the blocksize used to write the data.
PROPERTIES¶
Device drivers use properties as a generic means to interact with other parts of Amanda. Some properties are set by the device driver and used by Amanda to determine how its devices should be used. Other properties can be set by Amanda or by the user to influence the driver´s behavior. Properties are set for a particular device, so that if you have two tape devices, they will not share property values.
Properties are specified in amanda.conf with the device-property parameter. The syntax looks like this:
device_property "FROBNICATOR_PATH" "/var/frobd/state" device_property "BYTES_PER_FORTNIGHT" "128k" device_property "USE_QUBITS" "no"
Both the property name and the property value are always quoted. String values are given as simple strings, like FROBNICATOR_PATH in the example above. Integer values can be specified with any of the suffixes given in the "VALUE SUFFIXES" section of amanda.conf(5), like BYTES_PER_FORTNIGHT, above. Boolean values can be specified as any of "true", "yes", "1", "0", "no", "false", like USE_QUBITS, above. Some properties have special formats, as described below.
Some properties are set based on other configuration values, such as tapetype parameters. These special cases are detailed under the appropriate property, below.
The order in which device properties are set is as follows:
Properties described as read-only are not accessible to users. They are listed here for completeness.
COMMON PROPERTIES¶
Note that some of these properties are currently unused, and present only for future expansion. Not all devices implement all of these properties.
APPENDABLE
(read-only) This boolean property indicates whether this device supports
appending data to volumes.
BLOCK_SIZE
(read-write) This property gives the block size, in bytes, that will be used
to write to the device. The usual suffixes ("kbytes", etc.) are
allowed. The tapetype parameter blocksize sets this property.
CANONICAL_NAME
(read-only) This property contains the full canonical name for this device.
This name may not be the same as the user-supplied name, but is a valid name
by which to access this device.
COMPRESSION
(read-write) This boolean property represents the compression status of the
device, and can be used to enable and disable such compression. This applies
mostly to tape devices, although many tape devices do not support setting
compression from software.
COMPRESSION_RATE
(read-only) This property gives the compression rate, as a decimal ratio. It
may be a measured value over some unspecified period or a simple
estimate.
CONCURRENCY
(read-only) This property indicates the level of concurrent access that this
device supports.
FREE_SPACE
(read-only) This property gives the amount of free space available on the
current volume, if known. This is often an estimate; for example, tape
devices can only estimate the amount of tape left on a spool.
MAX_BLOCK_SIZE
(read-only) This property gives the maximum block size this device can
support. See BLOCK SIZES, below.
MEDIUM_ACCESS_TYPE
(read-only) This property gives the type of the media in the device: read
only, WORM (Write Once, Read Many), read/write, or write only. Write-only
devices do not support recovery, but the data are not necessarily thrown
out.
MIN_BLOCK_SIZE
(read-write) This property gives the minimum block size this device can
support. See BLOCK SIZES, below.
MAX_VOLUME_USAGE
(read-write) On devices that support it, this property will limit the total
amount of data written to a volume; attempts to write beyond this point will
cause the device to simulate "out of space." Zero means no limit.
The tapetype parameter length sets this property.
PARTIAL_DELETION
(read-only) This property indicates whether the device supports deletion of
specific files. Aside from linear tapes, most devices can support this
feature. It is currently unused by Amanda.
STREAMING
(read-only) This property gives the streaming requirement for this device.
For example, tape drives often require a steady supply of data to avoid
shoe-shining, while disk devices have no such requirement.
VERBOSE
(read-write) If this boolean property is set, then the device will produce
verbose debugging output. This property is not recognized by all
devices.
BLOCK SIZES¶
Amanda writes device data in blocks. On most devices the block boundaries are embedded in the media along with the data itself, so subsequent reads must use the same block sizes. On tape devices, the block size is dictated by the capabilities of the hardware -- buffer sizes, physical format, and so on.
Amanda has historically supported a single, fixed block size -- usually 32k. The Device API adds the ability to specify a block size at runtime, using the BLOCK_SIZE property. Devices provide MIN_BLOCK_SIZE and MAX_BLOCK_SIZE as a guide to the range of acceptable block sizes. Note that this does not imply that all sizes in the range MIN_BLOCK_SIZE - MAX_BLOCK_SIZE are available -- the device may require that block sizes are even multiples of some power of two, for example. Consult the documentation for your hardware and operating system for more information.
Most devices are flexible enough to read a volume using a different block size than that with which it was written. This can be useful when handling old volumes written with a smaller blocksize, or volumes of unknown blocksize. Unfortunately, some tape devices do not detect oversized blocks correctly, and may lose data if the configured block size is smaller than the volume´s block size. The tape device driver has a READ_BUFFER_SIZE property which specifies the minimum buffer size that will be allocated for reads from tape. If the hardware supports it, setting this property allows Amanda to correctly read from tapes written with any blocksize less than or equal to READ_BUFFER SIZE.
Note
The RAIT device does not support flexible block sizes, as its parity algorithm requires that all child devices have the same, fixed block size.
DRIVER-SPECIFIC PROPERTIES¶
S3 Device¶
S3_ACCESS_KEY
(read-write) This property gives the Amazon S3 access key used to access the
service.
S3_BUCKET_LOCATION
(read-write) Location constraint for buckets on Amazon S3. Currently, it can
be set to "", for no constraint (i.e. store data in the US), or
"EU" (i.e. store data in the EU). See Amazon´s
documentation for details and latest information
S3_SECRET_KEY
(read-write) This property gives the Amazon S3 secret key used to access the
service.
S3_SSL
(read-write) Whether or not to use SSL/TLS to secure communications with
Amazon S3.
S3_USER_TOKEN
(read-write) This property specifies the user token for Amanda Enterprise
Edition customers.
Most Amanda devices work just fine without any properties, but not the S3 device. A typical S3 configuration will have an access key and secret key specified:
device_property "S3_ACCESS_KEY" "27D3B8C6C4E7AA423C2B37C72A0D22C8" device_property "S3_SECRET_KEY" "agphc2Q7Zmxragphc2RmO2xragpzZGY7a2xqCgr"
Tape Device¶
Most of these properties are automatically detected, but can be overridden in the configuration file if the autodetection fails. Note that tape drives are required to at least support the MTREW (rewind) operation; all other operations can be emulated with the MTREW and read data operations.
BROKEN_GMT_ONLINE
(read-write) Set this boolean property if the system´s GMT_ONLINE
macro gives incorrect results. This is currently true for the Linux IDE-TAPE
driver.
BSF
(read-write) This boolean property specifies whether the device
driver may execute the MTBSF operation (backward seek file).
BSF_AFTER_EOM
(read-write) This boolean property specifies whether the device
driver should execute an MTBSF (backward seek file) operation after
MTEOM (seek to end of recorded data) in order to append.
BSR
(read-write) This boolean property specifies whether the device
driver may use the MTBSR operation (backward seek record).
EOM
(read-write) This boolean property specifies whether the device
driver may use the MTEOM command (seek to end of recorded data).
FINAL_FILEMARKS
(read-write) This integer property gives the number of filemarks that should
be written at EOD. It is usually 1 or 2.
FSF
(read-write) This boolean property specifies whether the device driver may
use the MTFSF operation (forward seek file).
FSF_AFTER_FILEMARK
(read-write) This boolean property specifies whether the device driver needs
a FSF to go the next file after the filemark is read. Default to
"TRUE" on Solaris and "FALSE" on all others
machines.
FSR
(read-write) This boolean property specifies whether the device driver may
use the MTFSR operation (forward seek record).
NONBLOCKING_OPEN
(read-write) Set this boolean property to "true" if O_NONBLOCK must
be used on the open call. Default to "true" on Linux and
"false" on all others machines. Witout it, Linux wait for a few
seconds if no tape are loaded. Solaris have strange error it is set to
"yes".
READ_BUFFER_SIZE
(read-write) This property specifies the minimum buffer size that will be
used for reads; this should be large enough to contain any block that may be
read from the device, and must be larger than BLOCK_SIZE. This property
exists for tape devices which cannot determine the size of on-tape blocks,
or which may discard data which overflows a small buffer. The tapetype
parameter READBLOCKSIZE sets this property. See BLOCK SIZES,
above.
SEE ALSO¶
AUTHORS¶
Ian Turner <ian@zmanda.com>
Dustin J. Mitchell <dustin@zmanda.com>
| 11/05/2009 | Amanda 2.6.1p2 |