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Software - MPE/iX 7.0 Operating System (1.13 mb)
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Resumen del manual
returned. (Disk DMs monitor “suspect” sectors and move/recover data to spare areas to avoid
data loss.)
Disks must guarantee ordered access. Simply put, if I write to a location on Disk first “A” next “B”
and then “C” in three distinct I/Os then when I read the data back it must be “C” not “B” or “A.”
SCSI disks typically support the multiple “in flight” I/Os and often have RAM buffer/caches to
store data; in both cases we want to be sure that I/Os are processed in the order that they are
sent.
MPE/iX SCSI Disk Drivers
When a device is added using SYSGEN/IOCONFIG, based on the device ID supplied, a physical
manager (pmgr, a.k.a Device Manager or DM) is assigned to the device. The DM used by a particular
device can be seen when a ‘lp’ (list path) of the device’s physical path is done. The following DMs
(pmgrs) in MPE/iX are specifically meant for disk drives:
scsi_disc_dm (SDM, for stand-alone disks),
scsi_disk_and_and_array_dm (SDARRAY, for disk arrays),
We can also use certain generic IDs to configure devices. For instance, a disk can be configured with
ID=LVDDISK, disk arrays with ID=HPDARRAY. The appropriate pmgr is set based on the ID.
SDM is the original SE-SCSI implementation for “disc” devices. It also allows interfacing with removable
media in the form of CD-ROM and Magneto-Optic disc devices.
This Device Manager is a single
threaded driver, only one SCSI I/O may be “active” at a time. Most typically this DM is configured for
devices that are connected via an HP28642A NIO SE-SCSI HBA (controlled by the scsi_dam) this implies
a “narrow” (8bit) “slow” (5-Mega-Transfers/ Second) connection.
SDA is a second generation SCSI-2 compliant disk device manager. This DM handles both JBOD and
Disk Array Products.
A key feature of this DM is that it can track and manage up to 8 “active” I/O
operations at a time. Originally this DM was designed to connect with the NIO F/W SCSI HBA HP28696A
for fast (10 Mega-Transfers/Sec), wide (16 bit), HVD (high voltage differential) devices. This driver was
later modified for SCSI devices connected through A/N-Class PCI-SCSI LVD&HVD HBAs (controlled by
pci_scsi_dam/c720) as well as the A6795A 2Gbit FC HBA (controlled by fc_dam/fcp_nm). This DM also
has embedded the majority of “High Availability Failover” code – this allows the DM to detect certain
problems with an I/O that may be due to HBA or physical path failure and “retry” the I/O on an alternate
HBA and physical path.
GDD Changes to the SCSI Disc Device Manager
There are two changes to this device manager during device initialization in the following areas:
a.
Asynchronous Event Notification
b.
PAGE 8 (cache settings)
a) Asynchronous Event Notification (AEN) – AEN is the ability of the discs to bring to the attention of the
I/O driver on asynchronous events like a disc getting ‘ready’ or it changing states. As per SCSI-2
standards, Discs support setting of two fields to indicate if AEN is enabled, READY_AEN_PERMISSION
and UNIT_ATTN_AEN_PERMISSION. To enable AEN on discs, the driver first checks if these fields can
be set. If not, AEN is not supported on the discs and hence is not enabled. If these fields are modifiable,
AEN is enabled.
...Otros modelos de este manual:
Software - MPE/iX 7.5 Operating System (26.44 kb)