Planning to Configure a Magneto-Optical Device

Characteristics of Magneto-Optical Devices

Magneto-optical devices yield good performance if data is distributed properly within its structural framework.

The size of an individual magneto-optical disk device makes it suitable for use as a boot disk, though its performance does not match that of a standard hard disk. Series 800 systems cannot be booted from magneto-optical devices.

Magneto-optical disk libraries contain multiple optical disks and multiple optical drives. HP offers several magneto-optical disk library products, with various capacity ranges and hardware configurations.

Each magneto-optical disk has two surfaces (sides), each of which appears to HP-UX as if it were an entire disk that can be used for a mountable file system or for raw access. Optical disk surfaces may be kept on- or off-line, as use requires. You may access simultaneously only as many autochanger surfaces are there are autochanger drives. (This is a change in implementation.) SAM will also allow access to only as many surfaces as there are drives.

	NOTE: If you exceed the number of drives, the request for the additional surface will either wait (sleep) without timeouts, or it will fail with an EBUSY error (indicating the device is currently busy). The resultant behavior depends on the specific operation. Requests to execute mount, mediainit, or newfs on surfaces will fail with an EBUSY error when all the drives are used. Other commands (such as raw access with cpio or dd) will wait (sleep) until a drive is available.

Understanding Magneto-Optical Media Capacity

Magneto-optical disk mechanisms support several different capacities:

HP-UX supports disks with 512 or 1024 bytes per sector, for both 1X and 2X capacity. Disks with 1024 bytes per sector give more storage space per disk, due to a smaller amount of sector overhead.

You can determine the media by executing the diskinfo command. diskinfo output for magneto-optical disks shows the information for the specific surface queried, not for the disk as a whole. The size in this example corresponds to the number of bytes on one surface of a 1X-capacity magneto-optical disk, with a sector size of 1024 bytes. (A 2X-capacity magneto-optical disk would show 581668 Kbytes.)

/usr/sbin/diskinfo /dev/rac/c0t1d0_4a
SCSI describe of /dev/rac/c0t1d0_4a:
             vendor: HP
         product id: C1716T
               type: optical memory
               size: 314568 Kbytes
   bytes per sector: 1024