mm_data(5)
mm_data(5)
NAME
mm_data - NetWorker media multiplexor data (tape and disk) format
DESCRIPTION
This documents the data format that the NetWorker media multiplexor
daemon, nsrmmd(8), writes to long term storage media such as tapes and
optical disks. See nsr_device(5) and nsrmm(8) for a discussion of sup-
ported device families and types. The format described here applies to
any fixed record device, such as raw disks, or fixed record tape
devices with file marks. NetWorker uses the eXternal Data Representa-
tion (XDR) standard to write media which can be interchanged among a
wide variety of machines. Only the mechanism used to multiplex save
set streams onto the storage media is described here; the formats of
save set streams depend on the type of NetWorker client, and are
described in nsr_data(5).
A volume is one physical piece of media such as a tape reel or disk
cartridge. A tape volume is made up of multiple media files, and each
media file may contain several media records. These media files and
records should not be confused with a client's (for example UNIX or
DOS) user files or records; the two do not necessarily correspond. For
example, a given media file or even a single media record may contain
many small client user files. On the other hand, a single large client
file may be split across several media files, and even across several
volumes. Media files do not span volume boundaries. Save sets may
span media files and even volumes.
On most tapes, media files can be skipped very quickly by the device's
hardware or associated device driver software, and the hardware can
detect when an end of a file has been reached. On some tapes, records
can also be quickly skipped forward. Otherwise, access to the media is
sequential.
Media records are described by the mrecord structure. Label records
are fixed in size, MINMRECSIZE bytes. Other records can potentially be
a larger size that must be some constant for the rest of the volume.
NetWorker always writes, reads and skips data in units of full-sized
media records. Each mrecord contains zero or more mchunks These
mrecords are used for storing one or more client save sessions or used
by NetWorker for synchronization and labelling. The XDR format of a
media file's mrecords and mchunks are as follows:
const MINMRECSIZE = 32768; /* minimum media record size */
const MMAXCHK = 2048; /* maximum number of chunks in record */
const MHNDLEN = 120; /* private area length for handlers */
enum mrec_version { /* mrecord version */
MREC_VER5 = 0, /* older format mrecord */
MREC_VER6 = 6 /* current format mrecord */
};
/*
* For media record format version 5, the data types lgui_t, lg_off64_t,
* and lg_time64_t are defined as:
*/
typedef struct lgui_t unsigned long;
typedef struct lg_off64_t unsigned long;
typedef struct lg_time64_t unsigned long;
/*
* For media record format version 6, the data types lgui_t, lg_off64_t,
* and lg_time64_t are defined as:
*/
typedef struct lgui_t { /* XDR encoded Unique Id. */
char _bytes[20];
} lgui_t;
typedef struct lg_off64_t unsigned long long;
typedef struct lg_time64_t unsigned long long;
typedef lgui_t ssid_t; /* save set id */
typedef lgui_t volid_t; /* key for the volume database */
struct mchunk {
ssid_t mc_ssid; /* owning save set id */
lg_off64_t mc_low; /* 1st byte, relative to save stream */
opaque mc_data<MINMRECSIZE>;/* chunk's data */
};
struct mrecord {
opaque mr_handler[MHNDLEN]; /* private to media handler */
mrec_version mr_version; /* Media record version number */
u_long mr_orec; /* record size */
volid_t mr_volid; /* encompassing volume's id */
u_long mr_fn; /* encompassing file number */
u_long mr_rn; /* record number within the file */
u_long mr_len; /* record byte length */
mchunk mr_chunk<MMAXCHK>; /* chunks of save streams */
};
The first field of an mrecord, mr_handler, is reserved for media-specific
data (currently it is not used by any implementation). The mr_version field
is the version number of the media record format. The size of the rest of
the fields in the media record depends on the version number. The mr_orec
field is the size of the current record. A media record's header fields,
mr_volid, mr_fn, and mr_rn, are used to check the tape position and the data
read from the record. The file numbers and record numbers start at
zero and increment sequentially. The record number is reset each time the
file number is incremented. On disks, file numbers are always zero.
The mr_len field is the actual number of valid bytes in this record, as opposed
to the size of the device's read or write request.
If file or record skipping is unreliable, NetWorker can still recover from
isolated errors, at worst by rewinding and reading the tape from the start.
If a volume can be physically unmounted or mounted without notice to the media
management daemon, then the volume identifier in each record provides a quick
way of verifying when this happens, without the need for a full rewind and
reading of the label in most cases.
The mchunks within an mrecord contain client data from one or more save sessions.
The mc_ssid and mc_low values are used to reconstruct the save streams from the
chunks within the records. The mc_data field holds the actual data of each chunk.
For a given save set, mc_low plus the length of mc_data should equal the following
chunk's value for mc_low. Save sets may by intermingled arbitrarily within media
records.
The first chunk of the first record of the first media file on the volume
encapsulates the volume label information; for some media, the second chunk
contains additional volume information, for example, the media pool the volume
belongs to: Subsequent data in the first file is reserved for future expan-
expansion. The label may be duplicated in a second
file for redundancy, in case the first copy of the label gets acciden-
tally overwritten. The formats of the volume label and additional
label information are described by the following XDR data structures:
const MVOLMAGIC = 0x070460; /* volume magic number */
const NSR_LENGTH = 64; /* length of several strings */
const RAP_MAXNAMELEN = 64; /* maximum length of attribute name */
struct mvollabel {
u_long mvl_magic; /* medium volume verification number */
lg_time64_t mvl_createtime; /* time at which volume labeled */
lg_time64_t mvl_expiretime; /* time for volume to expire */
u_long mvl_recsize; /* expected size of mrecords */
volid_t mvl_volid; /* medium volume id */
string mvl_volname<NSR_LENGTH>;/* medium volume name */
};
struct vallist {
vallist *next;
string value<>; /* attribute value */
};
struct attrlist {
attrlist *next;
string name<RAP_MAXNAMELEN>;/* attribute name */
vallist *values; /* attribute values */
};
/*
* Additional information may includes the following attributes
* (listed by the name they are stored with):
* "volume pool" : the media pool
*/
struct mvolinfo {
struct attrlist *mvi_attributes;/* any other information */
};
The mvl_magic field must be equal to MVOLMAGIC in order for the chunk to
represent a valid volume label. If the volume label changes in the future, the
new format will have another 'magic' number, but the format described here
must still be allowed. The mvl_volid is an internal identifier assigned and
managed by the media manager. The mvl_volname is the volume name that is
assigned when the media is first labeled. The time fields are in UST format -
the number of seconds elapsed since 00:00 GMT, January 1, 1970. The mvl_rec-
size is the size of all subsequent media records found on the tape.
The mvp_pool is the pool name that is assigned when the media is first
labeled. Different media pools allow administrators to segregate their data
onto sets of volumes. Media cannot be reassigned from one media pool to
another. Pool names are a maximum of NSR_LENGTH characters long.
Synchronization marks, called schunks, are also written periodically to the
media for each save set. Synchronization chunks are used by scanner(1) when
verifying or extracting directly from a volume. They are also used by nsrmmd
when trying to recover from media errors during file recovery. The following
XDR data structure describes a synchronization chunk:
typedef lgui_t clientid_t;
struct ssclone_t {
lg_time64_t ssc_cloneid; /* unique UST stamp wrt ss_ssid */
u_long ssc_flag; /* lots of status buried here*/
u_long ssc_frag; /* not used, always 0 */
};
/*
* Synchronization chunk of the newer MREC_VER6 media format.
*/
struct schunk {
u_long ssi_gen; /* Not used. */
ssid_t ssi_ssid; /* save set identifier */
ssid_t ssi_prev; /* non-zero iff continuation */
u_long ssi_level; /* backup level*/
lg_time64_t ssi_time; /* save time on client */
lg_time64_t ssi_create; /* creation time on server */
lg_time64_t ssi_insert; /* insertion time on server */
lg_time64_t ssi_complete; /* completion time on server */
clientid_t ssi_clientid; /* client name identifier */
u_long ssi_flags; /* more details about this ss */
string ssi_host<>; /* client name - save set owner */
string ssi_name<>; /* symbolic name, for example "/usr" */
uint64_t ssi_size; /* actual number of bytes saved */
uint64_t ssi_nfiles; /* number of client files saved */
u_long ssi_browse; /* browse time offset */
u_long ssi_recycle; /* recycle time offset */
struct attrlist *ssi_al; /* generic RAP attribute list */
ssclone_t ssi_clones<>; /* information about this clone */
};
/*
* Synchronization chunk of the older MREC_VER5 media format.
*/
struct old_schunk {
opaque ssi_host[NSR_LENGTH]; /* save set host */
opaque ssi_name[NSR_LENGTH]; /* symbolic name */
u_long ssi_time; /* save time */
u_long ssi_expiry; /* expiration date */
u_long ssi_size; /* actual size saved */
u_long ssi_nfiles; /* number of files */
ssid_t ssi_ssid; /* ssid for this save set */
u_long ssi_flag; /* various flags, see below */
u_long ssi_info; /* volid or ssid, see below */
};
#define SSI_START 1 /* start of a save set */
#define SSI_SYNC 2 /* synchronization point */
#define SSI_CONT 3 /* continued from another volume */
#define SSI_END 4 /* end of this save set */
#define SSI_SSMASK 0x0000000f /* save set sync chunk type */
#define SSI_LBIAS 0x10000000 /* the level is included in the flags */
#define SSI_LMASK 0xff000000 /* mask to cover bits for level */
#define SSI_LSHIFT 24 /* shift amount for the level */
#define SSI_INCOMPLETE 0x00010000 /* not finished (aborted) */
#define SSI_CONTINUED 0x00800000 /* continued save set series */
The ssi_ssid is the save set identifier of this save set. The ssi_time field
contains the create time of the save set in UST based on the client's clock.
The ssi_create field contains the create time of the save set in UST based on
the server's clock. The ssi_insert field contains the time the save set was
inserted into the media database in UST based on the server's clock. The
ssi_complete field contains the completion time of the save set in UST based
on the server's clock. The ssi_clientid and ssi_host are the client identi-
fier and name of the index which contains this save set. Traditionally this
is the client identifier and name of the client where the save set originated.
The ssi_name is the save set name to be presented to the user. These are both
null-terminated strings, even though the fields are fixed length in the older
version media records. The ssi_size and ssi_nfiles are the number of bytes
and number of files saved so far for this save set. The ssi_browse is the
time offset in seconds from the save set insertion time to the time this save
set is no longer browsable. The ssi_recycle is the time offset in seconds from
the save set insertion time to the time this save set becomes recyclable.
The ssi_al is the generic save set attribute.
The ssi_flag indicates the type of this synchronization chunk and other
information about the save set. In the older version synchronization
chunk, this field also contains the level of this save set. There are
four basic types of synchronization marks that can be found from exam-
ining ssi_flag & SSI_SSMASK. SSI_START is used to mark the beginning of a save
set. SSI_SYNC marks a periodic synchronization point and is only written at
an exact file boundary in the save set. SSI_CONT indicates that this is the
continuation of a save set that started on a different volume. When ssi_flag
& SSI_SSMASK is SSI_CONT, ssi_prev or ssi_info contains the volume identifier
for the save set's preceding volume. These synchronization chunks are used
when a save set spans a volume boundary. SSI_END marks the end of a save set.
On the new version of synchronization chunk, the ssi_level field contains the
save set backup level. On the older version of synchronization chunk. Should
the SSI_LBIAS bit be set then ssi_flag & SSI_LMASK shifted to the right by the
value of SSI_LSHIFT specifies the level of the save set. The SSI_INCOMPLETE
bit indicates that this save set did not finish properly. This could be
caused by a user interrupting an in progress save.
The SSI_CONTINUED bit indicates that this save set is logically continued to
or from another save set. These continued save sets are used to handle very
large save sets. If the SSI_CONTINUED bit is set and ssi_flag & SSI_SSMASK is
SSI_START, then ssi_prev or ssi_info gives the previous save set id that this
save set was continued from. If the SSI_CONTINUED bit is set and ssi_flag &
SSI_SSMASK is SSI_END, then ssi_prev or ssi_info gives the next save set id
that this save set is continued to.
The ssi_expiry field is the expiration date, in UST, for this save set. This
field is zero if an explicit save set expiration time was not specified when
the save set was created. This field no longer exists in the new synchroniza-
tion chunk.
SEE ALSO
nsr_device(5), nsr_data(5), nsrmm(8), nsrmmd(8), nsrmmdbd(8), nsr(8),
scanner(8).
RFC 1014 XDR: External Data Representation Specification
NetWorker 7.6.2 Jul 14, 11 mm_data(5)