Caching Write Data; Synchronized Spindle Operation; Figure 4. Synchronized Drive Interconnect Diagram - Seagate ST15150N - Barracuda 4.3 GB Hard Drive Product Manual

ST15150N/ND/W/WD/WC/DC Product Manual, Rev. D
5.6
5.7

Caching write data

Write caching is a drive write operation that uses a drive buffer storage area
where the data to be written to the disc is stored 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.
When a write command is issued, the cache is first checked to see if any
logical blocks 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 a 10-byte CDB Write command (2Ah) is issued with the data page out
(DPO) bit set to 1, no write data is cached, but the cache segments are still
checked and cleared, if needed, for any logical blocks that are being written
(see the SCSI-2 Interface Product Manual).
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 disc.

Synchronized spindle operation

The synchronized spindle 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 increase the system
capacity and transfer rate in a cost-effective manner.
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 4.
Note. ST15150WC/DC drives can use J6 pin 37 from the SCA connector
or J04 pin 6 for spindle sync.
Sync Interface
Master Sync
Source
Spindle
Control
Host
(or other drive)
+5V
Drive 1
System
Spindle
Interface
Control
+5V
Drive 2
Spindle
Control
+5V
Drive n
ST15150N/ND Drives

Figure 4. Synchronized drive interconnect diagram

Master Sync
J4
Source
1
Host
2
(or other drive)
R T
J4
System
1
Interface
2
R T
J4
1
2
R T
17
Sync Interface
J5
11
Spindle
Control
12
+5V
R T
Drive 1
J5
11
Spindle
Control
12
+5V
R T
Drive 2
J5
11
Spindle
Control
12
+5V
R T
Drive n
ST15150W/WD Drives