Phobos, standing for Parallel Heterogeneous OBject Store, is a tool designed to manage large volumes of data for various kinds of storage technologies from SSD to tapes. Phobos can efficiently handle very large datasets on inexpensive media without sacrificing scalability, performance, or fault-tolerance requirements.
Phobos is designed to allow the easy integration of new modules for layouts such as mirroring and erasure coding or, in a near future, I/O adapters.
This document presents basic information about Phobos installation and the first steps of its utilization. More information can be found in the following links:
You need to install LTFS >= 2.4 to enable phobos access to tapes.
LTFS RPM can be found on IBM Fix Central: ltfs 2.4
You can also retrieve its sources on gihub: https://github.com/LinearTapeFileSystem/ltfs
If you want to build RPMs from these sources, you can find packaging resources (i.e. spec file) for LTFS here: https://github.com/piste2750/rpm-ltfs
Note: since LTFS 2.4, lin_tape driver is no longer needed to access tapes.
LTFS now uses the standard linux tape driver (st).
Install phobos and its requirements:
yum install phobos
Install postgresql version >= 9.4 (from EPEL or any version compatible with Postgres 9.4):
yum install postgresql94-server postgresql94-contrib
Initialize postgresql directories:
/usr/pgsql-9.4/bin/postgresql94-setup initdb
Edit /var/lib/pgsql/9.4/data/pg_hba.conf to authorize access from phobos host
(localhost in this example):
# "local" is for Unix domain socket connections only
local all all trust
# IPv4 local connections:
host all all 127.0.0.1/32 md5
# IPv6 local connections:
host all all ::1/128 md5
Start the database server:
systemctl start postgresql-9.4.service
Finally, create phobos database and tables as postgres user (the password for SQL phobos user will be prompted for unless provided with -p):
sudo -u postgres phobos_db setup_db -s
To use phobos, a daemon called phobosd needs to be launched. It mainly manages the drive/media allocation and sets up resources to read or write your data.
To launch/stop the daemon:
# systemctl start/stop phobosd
Use the phobos lib scan command to scan a given library. For instance, the
following will give the contents of the /dev/changer library:
phobos lib scan /dev/changer
When using the library (such as when running the above command), if phobos returns an "invalid argument" error, and when you check the logs you see the following:
<WARNING> SCSI ERROR: scsi_masked_status=0x1, adapter_status=0, driver_status=0x8
<WARNING> req_sense_error=0x70, sense_key=0x5 (Illegal Request)
<WARNING> asc=0x24, ascq=0 (Additional sense: Invalid field in cbd)
<ERROR> Sense key 0x5 (converted to -22): Invalid argument
<ERROR> scsi_element_status failed for type 'drives': Invalid argument
It may be a tape library limitation. For some type of tape libraries, for instance IBM libraries, one can't query a drive's serial number and it's volume label in the same request. To prevent this, phobos can separate the query in two by activating the parameter 'sep_sn_query' in the section 'lib_scsi', as shown here, or as the environment variable 'PHOBOS_LIB_SCSI_sep_sn_query=1'.
Use the phobos command line to add new tape drives to be managed by phobos.
It is recommanded to specify a device path which is persistent after reboot (eg. managed by dev mapper).
By default, drives are added in a locked state, so they are not immediatly used in production.
To enable using a drive in production as soon as it is added, specify the '--unlock' option:
phobos drive add --unlock /dev/mapper/LTO6-012345
To add tapes to be managed by phobos, use the phobos command line.
It is mandatory to specify a media type (like LTO8, T10KD...) with option -t:
phobos tape add --type lto6 [073200-073222]L6
Note1: this operation requires no access to the medium.
Note2: the set of supported media types, drive types, and compatibility rules between drives and media are configurable. See section 'Configuring device and media types' below for more details.
Once a media has been added, it needs to be formatted. You can optionally unlock the tape when the operation is done, so it becomes usable in production.
phobos tape format --unlock 073200L6
A device or media can be locked. In this case it cannot be used for subsequent 'put' or 'get' operations:
phobos drive {lock|unlock} <drive_serial|drive_path>
phobos media {lock|unlock} <media_id>
Any device or media can be listed using the 'list' operation. For instance, the following will list all the existing tape identifiers:
phobos tape list
The rest of this document will describe object management using CLI calls. An API is available and is more described here.
When pushing an object you need to specify an identifier that can be later used to retrieve this data.
Phobos also allows specifying an arbitrary set of attributes (key-values) to be attached to the object. They are specified when putting the object using the '-m' option.
# phobos put <file> <id> --metadata <k=v,k=v,...>
phobos put myinput_file foo-12345 --metadata user=$LOGNAME,\
put_time=$(date +%s),version=1
To retrieve the data of an object, use phobos get. Its arguments are the
identifier of the object to be retrieved, as well as a path of target file.
For example:
phobos get obj0123 /tmp/obj0123.back
To retrieve custom object metadata, use phobos getmd:
$ phobos getmd obj0123
cksum=md5:7c28aec5441644094064fcf651ab5e3e,user=foo
To delete an object, use phobos del[ete]:
phobos del obj0123
WARNING: the object will not be completely removed from the phobos system ie. its data will still exist and be accessible. Thus the object is considered as deprecated and basic operations can no longer be executed on it if its uuid/version is not given. A future feature will allow the complete removal of an object.
This deletion can be reverted using phobos undel[ete]:
phobos undel obj0123
To revert an object deletion, the object ID needs not to be used by a living object.
To list objects, use phobos object list:
$ phobos object list --output oid,user_md
| oid | user_md |
|-------|-----------------|
| obj01 | {} |
| obj02 | {"user": "foo"} |
The --output option describes which field will be output. all can be used as
a special field to select them all.