Seagate ST31200N, Руководство по эксплуатации продукта

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14 Product Manual - Hawk 1LP Family SCSI-2 (Volume 1), Rev. B
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5.6 Caching write data
Write caching is a write operation by the drive that makes use of a drive buffer storage area where the data
to be written to the medium is stored in one or more segments while the drive performs the write command.
Write caching is enabled along with read caching. For write caching, the same buffer space and segmentation
is used as set up for read functions. The buffer segmentation scheme is set up or changed independently,
having nothing to do with whether or not read and write caching is enabled or disabled. When a write command
is issued, the cache is first checked to see if any logical blocks that are to be written are already stored in the
cache from a previous read or write command. If there are, the respective cache segments are cleared. The
new data is cached for subsequent Read commands.
If the number of write data logical blocks exceeds the size of the segment being written into when the end of
the segment is reached, the data is written into the beginning of the same cache segment, overwriting the data
that was written there at the beginning of the operation. However, the drive does not overwrite data that has
not yet been written to the medium.
Tables 11.3.2-1 through 11.3.2-4 show Mode default settings for the Hawk 1LP family drives.
5.7 Synchronized spindle operation
The synchronized spindles operation allows several drives operating from the same host to operate their
spindles at the same synchronized rotational rate. Drives operating in a system in synchronized mode can
increase the system capacity and transfer rate in a cost effective manner.
For Hawk 1LP models, the interface consists of a twisted pair cable that connects the drives in the synchronized
system in a daisy-chain configuration as shown in Figure 5.7-1. For "NC" models, the reference index signal
(SYNC) signal is on pin J1-37 of the 80-pin I/O connector. See Table 11.6.3-1c. Master/Slave operation is
autoarbitrated by each drive after head load. Alternatively, each drive in the system can be configured by the
host (using the Mode Select command Rigid Disc Drive Geometry page*) to operate in either the master or
slave mode.
After loading heads, a drive autoarbitrates for occurences of the Reference Index Signal (). If the drive
detects no signal on the line, it assumes master status and begins generating the signal.
This signal will not be visible on the line until the last drive has powered up, since any unpowered drive holds
the line low.
Using Mode Select command, drives can be re-configured by the host to be master or slave any time after the
last drive has powered up. The master provides the reference signal to which all other drives phase lock,
including the master. The master can be a drive or the host computer. All the drives may be configured as
slaves, allowing the host to provide the signal. All drives default to the synchronized mode when
powered up, unless J6 pins 5 and 6 are jumpered.
Each drive can be configured (jumpered) for the non-synchronized mode in which it ignores any reference
signal that might be present. The connection of the synchronized reference signal to the host is required only
if the host is to provide the reference signal. If the host does not provide the reference signal, the host should
not be connected.
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*SCSI Interface Product Manual P/N 77738479