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Additional Notes

2-39

Installing and Configuring the HBA and Driver

In total, a Red Hat host could support disk devices from /dev/sda

through

/dev/sddx.

SuSE Distributions

For SuSE distributions prior to SLES 8, the limitations are the same as

for Red Hat distributions. SuSE SLES 8 is different in that it supports

up to 256 devices by default as it reserves 16 major numbers for SCSI

devices.

Each major number is allocated 0 to 255 minor numbers that are used

to denote the partitions for a SCSI device. Therefore, a product of 16

major numbers and 16 minor numbers yields up to 256 SCSI devices.

As a result, the kernel is able to scan logical devices ranging from 0

through 255. These disk devices would be reported as

/dev/sda

through /dev/sdiu.

Therefore, if you have allocated LUNs from 0 through 255 to the

SLES 8 Linux host, the host can scan and use all 256 logical units.

However, just as with Red Hat distributions, if you present logical

units over 256 to a Linux host, the host will neither see nor be able to

access those devices with an address of over 256.

PowerPath Examples

If you have EMC PowerPath

installed, keep in mind that there is a

limitation of 128 SCSI devices total per system, not per adapter.

◆ Example without PowerPath — If you have two HBAs or a dual

channel HBA and you want both ports/HBAs to see and access

devices, you must split the 128 devices between the two HBAs.

For example, 64 devices would be allocated to each HBA. If you

allocate 128 devices to the first HBA, the second HBA will not be

able to access any devices. The limitation of 128 SCSI devices is in

the Linux SCSI subsystem and is per system, not per adapter.

◆ Example with PowerPath — Keep in mind that if you present 128

LUNs to a Linux host to one HBA, then only that one HBA will be

able to see and access devices.

In the case of PowerPath, if you have eight HBAs in a server and

plan to have two paths per HBA, you will be left with only eight

devices per HBA:

128 LUNs/ (8 HBAs * 2 paths) = 8 devices

QLogic_Linux.book Page 39 Monday, November 1, 2004 2:15 PM

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Dell QLA2200 Guía de instalación Pagina 51