autochanger(7) autochanger(7)
NAME [Toc] [Back]
autochanger - SCSI interfaces for medium changer device and magnetooptical
autochanger surface device
DESCRIPTION [Toc] [Back]
An autochanger is a SCSI mass storage device, consisting of a
mechanical changer device, one or more data transfer devices (such as
optical disk drives), and media (such as optical disks) for data
storage. The mechanical changer moves media between storage and usage
locations within the autochanger.
Depending on system architecture, one of two medium changer drivers
(schgr or autox0) provides access to the medium changer device; a
module (ssrfc) provides access to the surfaces of the optical disks.
Two levels of functionality are provided by the medium changer
drivers. The mechanical changer device can be accessed directly to
move media within the autochanger. Alternatively, media surfaces can
be accessed as unique devices, causing the changer driver to move the
media into a drive to perform an I/O request.
The schgr and autox0 medium changer device drivers follow the SCSI
specification for medium changer devices to provide a generic medium
changer interface, making it feasible to construct an application
level driver for any mechanical changer, jukebox, library, or
autochanger device (MO, tape, CD-ROM).
However, the ssrfc module is provided specifically to support
Hewlett-Packard magneto-optical disk autochanger products.
Device Naming Convention [Toc] [Back]
The device naming convention for the autochanger driver enables
accessing the changer device, as well as individual media surfaces.
Block devices for autochangers reside in /dev/ac, character devices
reside in /dev/rac. Within these directories, names are derived from
the "c#t#d#" device naming convention (explained in intro(7)), with
the surface descriptor appended at the end. Unique device names are
determined by the card instance, target address of the SCSI changer
device, LUN of the SCSI changer device, and the surface descriptor.
The surface descriptor can be zero or non-specified for the changer
device. Also, there is no block special file for the changer itself.
For example,
/dev/rac/c1t5d0
is the character special file for the changer at SCSI target address 5
and LUN 0, attached to SCSI card instance 1, and is equivalent to
/dev/rac/c1t5d0_0.
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Any given surface is described by the card instance, SCSI target
address and SCSI LUN of the changer, and then appended with a surface
descriptor for the slot number and side. For example,
/dev/ac/c1t5d0_1a
is the block special file for surface 1a of the autochanger just
mentioned and
/dev/rac/c1t5d0_1a
is the character special file for the same surface 1a.
Major and Minor Number Descriptions [Toc] [Back]
The following shows the bit assignments (dev_t format) used by the
changer drivers to access the changer device and each surface within
an autochanger:
+-------+-------+-------+-------+--------+------+--+----------------+
| 0 | 7| 8 15|16 19|20 22|23 31|
+-------+-------+-------+-------+--------+------+--+----------------+
| MAJOR | INSTANCE | TARGET | LUN | SURFACE |
+-------+-------+-------+-------+--------+------+--+----------------+
MAJOR is the major number of the appropriate driver, INSTANCE is the
card instance of the SCSI interface to which the changer device is
attached, TARGET is the SCSI target address of the changer device, LUN
is the SCSI LUN of the changer device, and SURFACE is the unique
descriptor of each surface in the autochanger, as described in the
following table. (Note, the surface descriptors refer to bits 23-31.)
+----------------+--------------------+
| Surface | Surface descriptor |
+----------------+--------------------+
| changer device | 00 |
| 1a | 01 |
| 1b | 02 |
| 2a | 03 |
| 2b | 04 |
| ... | ... |
| 31b | 3e |
| 32a | 3f |
| 32b | 40 |
| .... | .... |
+----------------+--------------------+
All fields in the device number are specified in hexadecimal notation.
Note that there is no support for hard partitions (sections) in this
minor number. If desired, partitioning can be achieved via LVM soft
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partitioning schemes.
The major numbers used by the changer drivers are:
b_major | c_major |
+---------+---------+
schgr | 29 | 231 |
autox0 | 30 | 230 |
+---------+---------+
Following are long listings showing the major and minor numbers
associated with the device special file names of the first surface and
the changer:
schgr:
brw-rw-rw- 1 root sys 29 0x015001 Apr 22 10:22 /dev/ac/c1t5d0_1a
crw-rw-rw- 1 root sys 231 0x015001 Apr 22 10:22 /dev/rac/c1t5d0_1a
crw-rw-rw- 1 root sys 231 0x015000 Apr 22 10:22 /dev/rac/c1t5d0
autox0:
brw-rw-rw- 1 root sys 30 0x015001 Apr 24 11:35 /dev/ac/c1t5d0_1a
crw-rw-rw- 1 root sys 230 0x015001 Apr 24 11:35 /dev/rac/c1t5d0_1a
crw-rw-rw- 1 root sys 230 0x015000 Apr 24 11:35 /dev/rac/c1t5d0
MAGNETO-OPTICAL AUTOCHANGER SURFACE DEVICE ACCESS [Toc] [Back]
To access disk surfaces within HP magneto-optical libraries, it is
necessary to include the entry for the surface module, ssrfc, in the
system configuration file /stand/system, as well as an entry for the
appropriate SCSI changer driver, schgr or autox0, depending on
architecture. The ssrfc module enables accessing a magneto-optical
disk surface much like a disk device. The disk is moved into an idle
drive by the changer, then the requested disk I/O operation is
performed. Upon completion of the request, the disk is returned to
its storage location within the autochanger.
The surface module allows concurrent access to as many disks as there
are drives in the autochanger product. Requests for I/O on additional
disks within the autochanger are blocked awaiting an available drive
resource.
By default, some commands (such as mount, newfs, and mediainit) open
the device with the O_NDELAY flag set. Invocations of these commands
on an autochanger surface do not wait for a drive resource to become
available. Instead, these requests return with [EBUSY] if no drive is
available.
Developers using the surface module functionality to access
autochanger disks can invoke the open system call with the O_NDELAY
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flag to achieve this same "non-blocking" behavior:
error = open("/dev/rac/c1t5d0_1a",O_RDWR | O_NDELAY);
If it is acceptable to block waiting for an available drive resource,
the O_NDELAY flag is unnecessary.
Here is a sample script to access multiple disk surfaces in an
autochanger that has 2 drives, minimizing blocking:
dd if=/dev/rdsk/c0t0d0 of=/dev/rac/c1t5d0_1a bs=64k &
dd if=/dev/rdsk/c0t1d0 of=/dev/rac/c1t5d0_2a bs=64k &
wait
dd if=/dev/rdsk/c0t2d0 of=/dev/rac/c1t5d0_1b bs=64k &
dd if=/dev/rdsk/c0t3d0 of=/dev/rac/c1t5d0_2b bs=64k &
wait
...
For developers, the ioctl functions available for accessing magnetooptical
disk surfaces are described in the manual pages for SCSI disk
drivers. Several ioctl functions provided specifically for magnetooptical
disks will be described here briefly. Included from
<sys/scsi.h>:
#define SIOC_WRITE_WOE _IOW('S', 17, int)
#define SIOC_VERIFY_WRITES _IOW('S', 18, int)
#define SIOC_ERASE _IOW('S', 19, struct scsi_erase)
#define SIOC_VERIFY_BLANK _IOW('S', 20, struct scsi_verify)
#define SIOC_VERIFY _IOW('S', 21, struct scsi_verify)
SIOC_ERASE (erase) and SIOC_WRITE_WOE (write without erase) can be
used together on character special devices. By performing a pre-erase
pass of magneto-optical disks, then later setting the SCSI disk driver
in write-without-erase mode, improved write performance can be
achieved, eliminating the two-pass erase-then-write which is normally
necessary on magneto-optical devices.
SIOC_VERIFY_WRITES (write and verify) performs a verification pass on
any writes to magneto-optical disks. This is a good safeguard for
data integrity. However, write operations performed with the
verification pass exhibits a decrease in performance. When used with
pre-erase and write-without-erase, write and verify provide increased
reliability of data without decreased performance. HP recommends
operating in write-and-verify mode if also performing write-withouterase.
The following are additional ioctl functions that might be desirable
for some magneto-optical products, included from <sys/scsi.h>:
#define SIOC_GET_IR _IOR('S', 14, int)
#define SIOC_SET_IR _IOW('S', 15, int)
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#define SIOC_SYNC_CACHE _IOW('S', 70, int)
SIOC_GET_IR determines the current state of immediate reporting (write
caching) on the device. SIOC_SET_IR enables or disables immediate
reporting on the device. If SIOC_SET_IR is used to enable write
caching, it may be desirable to flush the write cache using the
SIOC_SYNC_CACHE ioctl function. The command /usr/sbin/scsictl may be
used to perform the pre-erase of magneto-optical disks, set and check
the status of immediate reporting.
With the surface module configured, several ioctl functions to get
status and information from the changer device are also available.
These are SIOC_ELEMENT_ADDRESSES, SIOC_ELEMENT_STATUS, and
SIOC_INQUIRY; they are explained further in the following section on
the changer driver. Functions that modify the state of the
autochanger are not allowed when the surface module is configured into
the kernel.
SCSI MEDIUM CHANGER DEVICE DRIVER [Toc] [Back]
The SCSI medium changer device driver performs moves between different
media locations within an autochanger. Each potential media location
has a specific element address and is one of the following element
types:
storage A location to hold a unit of media not
currently in use. Typically most media will
be located in this type of element.
import/export A location for inserting and removing media
from the device. Movement of a unit of media
to this type of location is in effect an
eject operation. Movement of a unit of media
from this type of location is a load
operation.
data transfer A location for accessing media data. This is
generally the location of a device that reads
and/or writes data on the media being handled
by the media changer device. Movement to
this type of location is a physical-mediamount
operation. Movement from this type of
location is a physical-media-unmount
operation.
media transport A location for media movement. Media is
generally temporarily located in this type of
element only during actual media movement.
Changer Control Requests [Toc] [Back]
The following ioctl functions are included from <sys/chgrio.h>:
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#define CHGR_SSRFC_IS_PRESENT _IOR('X', 1, int)
#define CHGR_CLEAR_RESET _IO('X', 2)
CHGR_SSRFC_IS_PRESENT [Toc] [Back]
For developers. To determine if the surface module functionality
(ssrfc) is currently configured in the kernel.
CHGR_CLEAR_RESET [Toc] [Back]
For developers. autox0 driver only. To clear a powerfail
recovery condition in the SCSI changer driver. The
CHGR_CLEAR_RESET ioctl function will be necessary for developers
using the SCSI changer driver (autox0) to move media within the
medium changer, but not using the surface module for transparent
access to magneto-optical disks. In the event of an [ECONNRESET]
error return from any changer ioctl call, a CHGR_CLEAR_RESET call
will be necessary prior to any further media moves. This alerts
the application of a possible power failure, and allows the
developer an opportunity to reset data structures, and re-reserve
elements in the medium changer, prior to further operations.
The following ioctl functions and structure definitions are included
from <sys/scsi.h>:
#define SIOC_INIT_ELEM_STAT _IO('S', 51)
#define SIOC_ELEMENT_ADDRESSES _IOW('S', 52, struct element_addresses)
#define SIOC_ELEMENT_STATUS _IOWR('S', 53, struct element_status)
#define SIOC_RESERVE _IOW('S', 54, struct reservation_parms)
#define SIOC_RELEASE _IOW('S', 55, struct reservation_parms)
#define SIOC_MOVE_MEDIUM _IOW('S', 56, struct move_medium_parms)
#define SIOC_EXCHANGE_MEDIUM _IOW('S', 57, struct exchange_medium_parms)
/* structure for SIOC_ELEMENT_ADDRESSES ioctl */
struct element_addresses {
unsigned short first_transport;
unsigned short num_transports;
unsigned short first_storage;
unsigned short num_storages;
unsigned short first_import_export;
unsigned short num_import_exports;
unsigned short first_data_transfer;
unsigned short num_data_transfers;
};
/* structure for SIOC_ELEMENT_STATUS ioctl */
struct element_status {
unsigned short element; /* element address */
unsigned int resv1:2;
unsigned int import_enable:1; /* allows media insertion (load) */
unsigned int export_enable:1; /* allows media removal (eject) */
unsigned int access:1; /* transport element accessible */
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unsigned int except:1; /* is in an abnormal state */
unsigned int operatr:1; /* medium positioned by operator */
unsigned int full:1; /* holds a a unit of media */
unsigned char resv2;
unsigned char sense_code; /* info. about abnormal state */
unsigned char sense_qualifier; /* info. about abnormal state */
unsigned int not_bus:1; /* transfer device SCSI bus differs */
unsigned int resv3:1;
unsigned int id_valid:1; /* bus_address is valid */
unsigned int lu_valid:1; /* lun is valid */
unsigned int sublu_valid:1; /* sub_lun is valid */
unsigned int lun:3; /* transfer device SCSI LUN */
unsigned char bus_address; /* transfer device SCSI address */
unsigned char sub_lun; /* sub-logical unit number */
unsigned int source_valid:1; /* source_element is valid */
unsigned int invert:1; /* media in element was inverted */
unsigned int resv4:6;
unsigned short source_element; /* last storage medium location */
char pri_vol_tag[36]; /* volume tag (device optional) */
char alt_vol_tag[36]; /* volume tag (device optional) */
unsigned char misc_bytes[168]; /* device specific */
};
/* structure for SIOC_RESERVE and SIOC_RELEASE ioctls */
struct reservation_parms {
unsigned short element;
unsigned char identification;
unsigned char all_elements;
};
/* structure for SIOC_MOVE_MEDIUM ioctl */
struct move_medium_parms {
unsigned short transport;
unsigned short source;
unsigned short destination;
unsigned char invert;
};
/* structure for SIOC_EXCHANGE_MEDIUM ioctl */
struct exchange_medium_parms {
unsigned short transport;
unsigned short source;
unsigned short first_destination;
unsigned short second_destination;
unsigned char invert_first;
unsigned char invert_second;
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};
SIOC_INIT_ELEM_STAT [Toc] [Back]
Cause the media changer device to take inventory. As a result,
the media changer device determines the status of each and every
element address, including the presence or absence of a unit of
media. This is a mechanical operation which can take time. This
function only necessary in the event of a severe error of the
media changer. If using the surface module (ssrfc) to move disks,
this level of error recovery is handled within the surface
module.
SIOC_ELEMENT_ADDRESSES [Toc] [Back]
Determine the element addresses supported by a media changer
device. The first valid element address and the number of
elements is indicated for each element type. These element
addresses may be used as source and destination location
arguments.
SIOC_ELEMENT_STATUS [Toc] [Back]
Determine the status of an element. The element address for
which status information is requested is specified via the
element field. The resulting status data indicates the presence
or absence of a unit of media in that element address as well as
other information about the element address.
SIOC_RESERVE and SIOC_RELEASE
Control access to element addresses. Depending on the device,
reservations may limit operator control of those element
addresses in the media changer device. Specific element
addresses can be reserved to handle interlocking between multiple
requesters if each requester has a unique reservation
identification. The value zero in the all_elements field
specifies that a single element address should be reserved or
released. An element address reserved in this manner can not be
reserved by another single element address reservation using a
different reservation identification. The reservation field
specifies the reservation identification. The element field
specifies the element address to be reserved.
The value ``1'' in the all_elements field indicates that all
element addresses should be reserved. The reservation and
element fields should contain the value zero since these fields
are not meaningful when reserving all element addresses.
Reserving all element addresses is primarily useful for limiting
operator control.
SIOC_MOVE_MEDIUM and SIOC_EXCHANGE_MEDIUM
Reposition unit(s) of media. Depending on the source and
destination element types, this may result in a media load,
eject, or simple repositioning. Media can be ``flipped'' using
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values of ``1'' in the invert, invert_first, or invert_second
fields. The SIOC_EXCHANGE_MEDIUM ioctl repositions two different
units of media. One unit of media is moved from the element
specified by the source field to the element specified by the
first_destination field. A second unit of media is moved from
the element specified by the first_destination field to the
element specified by the second_destination field. In an
autochanger with multiple changer mechanisms, or a media staging
area, an exchange occurs if the source and second_destination
fields are the same.
DEPENDENCIES [Toc] [Back]
To obtain access to disk surfaces within HP magneto-optical libraries,
the ssrfc module must be specified in the system configuration file.
The ssrfc module depends on either the schgr driver, or the autox0
driver. If ssrfc is to be included, then one or both of schgr or
autox0 must also be included.
DEFAULT CONFIGURATIONS [Toc] [Back]
By default, ssrfc, schgr, and autox0 are not included in the system
configuration (/stand/system) file.
EXAMPLES [Toc] [Back]
The following example uses the SIOC_ELEMENT_ADDRESSES and
SIOC_ELEMENT_STATUS ioctl functions to get bus address information
about the drives in an HP magneto-optical autochanger:
int last_drive_el;
struct element_addresses el_addrs;
struct element_status el_stat;
/*
* Changer attached to card instance 1, with SCSI target id 5, lun 0.
*/
fd = open("/dev/rac/c1t5d0",O_RDWR);
if ((error = ioctl(fd, SIOC_ELEMENT_ADDRESSES, &el_addrs)) != 0) {
syserr("ioctl: SIOC_ELEMENT_ADDRESSES");
return -1;
} else {
last_drive_el = el_addrs.first_data_transfer
+ el_addrs.num_data_transfers - 1;
for (i = el_addrs.first_data_transfer; i <= last_drive_el; i++) {
el_stat.element = i;
if ((error = ioctl(fd, SIOC_ELEMENT_STATUS, &el_stat)) != 0) {
syserr("ioctl: SIOC_ELEMENT_ADDRESSES");
return -1;
} else {
/*
* You may wish to also check some of the other fields
* in the el_stat structure to verify that the data is
* valid. Fields: el_stat.access (ac accessible),
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* el_stat.except (exception).
*/
if (! el_stat.not_bus && el_stat.id_valid) {
drive[i].addr = el_stat.bus_address;
if (! el_stat.lu_valid) {
drive[i].lun = 0;
} else {
drive[i].lun = el_stat.lun;
}
}
}
}
}
WARNINGS [Toc] [Back]
Do not use LVM to configure multiple autochanger surfaces as one large
file system. LVM was designed for on-line volumes. In an autochanger,
only the disks actualy in the drives are on-line, while the disks
stored in their slots are off-line. If LVM is not carefully
configured, thrashing of the autochanger disks result in undesirable
I/O performance. Plan carefully for best performance.
Some non-HP media changer devices do not support the
SIOC_INIT_ELEM_STAT and SIOC_ELEMENT_STATUS ioctls.
Some older media changer devices do not support the
SIOC_EXCHANGE_MEDIUM ioctl. For these devices, multiple
SIOC_MOVE_MEDIUM ioctl operations may be used to accomplish the same
results, provided a suitable temporary element address may be found.
SEE ALSO [Toc] [Back]
insf(1M), mknod(1M), scsictl(1M), ioctl(2), scsi(7), scsi_ctl(7).
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