IBM DS4700 manual Total number

The problem with soft AL_PAs addressing is that addresses may change between LIPs. This possibility increases the difficulty of troubleshooting drive channel problems, since one cannot easily ascertain whether the same device with a different address or different device may be causing a problem. IBM recommends always setting the enclosure IDs in a given drive channel/loop pair to enforce hard AL_PAs addressing.

Intermixing storage expansion enclosures in the same drive loop

In a DS4700 Express configuration, you can intermix EXP810s, EXP710s, and EXP100s. When intermixing EXP810s with EXP710s or EXP100s in the same drive loop, the Link Rate switch for all storage expansion enclosures in the intermixed drive loop must be 2 Gbps because the EXP710 and EXP100 only operate at 2 Gbps.

There are maximum limits to the number of fibre channel hard drives that you can configure in redundant drive channel pairs. The maximum number of drives dictates a fixed number of supported EXP710 or EXP100 and EXP810 drive enclosure combinations.

Table 31 lists the numbers of 14-drive and 16-drive storage expansion enclosures you can combine for use in a single redundant drive channel/loop pair in a DS4700 Express configuration. Table 31 shows the supported storage expansion enclosures combinations per redundant drive channel/loop pair in a DS4700 Express configuration. The table assumes that a DS4700 Express storage subsystem is generally capable of addressing the maximum of 112 fibre channel hard drives for each redundant drive channel/loop pair.

Table 31. Possible combinations of 14-drive and 16-drive storage expansion enclosures per redundant drive/channel loop pair in a DS4700 Express configuration

						Total number
		Number of	Total	Total		of drives in a
Number of	Total	EXP710/	number of	number of		mixed
EXP810s	number of	EXP100s	drives in	drives in		EXP710s and
(16	drives in	(14	EXP710/	the DS4700		EXP810s drive
drives/unit)	EXP810s	drives/unit)	EXP100s	Express		loop
0	0	7	98	16	=	114
1	16	5	70	16	=	102
2	32	4	56	16	=	104
3	48	3	42	16	=	106
4	64	2	28	16	=	108
5	80	1	14	16	=	110
6	96	0	0	16	=	112

For more information about intermixing storage expansion enclosures and the most current information on the DS4000 Fibre Channel and Serial ATA (FC/SATA) Enclosure Intermix premium feature, see the following Web site:

www-1.ibm.com/support/docview.wss?rs=1100&uid=psg1MIGR-57823

Chapter 3. Cabling the storage subsystem 99