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mm_data - NetWorker media multiplexor data (tape and disk) format


       This  documents  the  data  format that the NetWorker media multiplexor
       daemon, nsrmmd(1), writes to long term storage media such as tapes  and
       optical disks.  See nsr_device(5) and nsrmm(1) 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

       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 {         /* 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

	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
	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 */
    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" */
    lg_uint64_t ssi_size;          /* actual number of bytes saved */
    lg_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
	SSI_START is used to mark the beginning of a save set.  SSI_SYNC marks a peri- 
	odic  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 preced- 
	ing  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.


       nsr_device(5), nsr_data(5), nsrmm(1), nsrmmd(1), nsrmmdbd(1), nsr(1),

       RFC 1014 XDR: External Data Representation Specification


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