Originally posted by: GregL.

This is driving me nuts as we used to be able to do this....

There used to be way to change the link speed of FC adapters (Qlogic) but the attribute seems to be missing now.

If memory serves it used to be something along the lines of chdev -l fcs0 -a link_speed= (Or possible data_rate)

The issue we seem to be having is even though we have fixed the speed in open firmware AIX is still saying it's Auto, and we need it fixed due to various link issues we're having (BladeCenter 8G problems)

Any ideas?

Originally posted by: shargus

Don't know if this helps, but we always leave the AIX side set to "auto" and set the link speed on the switch side.

Doing that, we've never had problems with AIX figuring out the correct link speed.

Probably better to do it that way, than to risk having AIX set to a link speed that's different from the switch's link speed...

Originally posted by: hdkutz

Hello,
i use this to change my speed settings in AIX:
<snip>
#######################

1. fiberchannel settings

#######################

1. show settings of an attribute
2. lsattr -El fcs0

bus_intr_lvl 323 Bus interrupt level False
bus_io_addr 0xdf800 Bus I/O address False
bus_mem_addr 0xe8081000 Bus memory address False
init_link al INIT Link flags True
intr_priority 3 Interrupt priority False
lg_term_dma 0x800000 Long term DMA True
max_xfer_size 0x200000 Maximum Transfer Size True
num_cmd_elems 200 Maximum number of COMMANDS to queue to the adapter True
pref_alpa 0x1 Preferred AL_PA True
sw_fc_class 2 FC Class for Fabric True

1. lsattr -El fcs0 -R -a max_xfer_size

0x100000
0x200000
0x400000
0x800000
0x1000000

1. change direct (vol must be offline)
2. chdev -l fcs0 -a max_xfer_size=0x200000

1. odm change only
2. chdev -l fcs0 -P -a max_xfer_size=0x100000 (default)
3. chdev -l fcs0 -P -a max_xfer_size=0x200000 # 2GB
4. chdev -l fcs0 -P -a max_xfer_size=0x400000 # 4GB
5. chdev -l fcs0 -P -a max_xfer_size=0x800000 # 8GB
6. chdev -l fcs0 -P -a max_xfer_size=0x1000000 # 10GB
7. chdev -l fcs0 -P -a lg_term_dma=0x800000 (0x800000)

Reboot to make changes active.
<snip>

HTH,
ku

Originally posted by: 9GWD_Shannon_Moore

The comment which says to increase max_xfer_size in order to 'increase speed" is absolutely wrong.  The max_xfer_size attribute has nothing to do with the adapter speed.  Rather max_xfer_size dictates the limit for the maximum SIZE of an individual I/O sent by the adapter port.

 

Increasing max_xfer_size results in more DMA space being allocated to the adapter.  Setting this value too high can actually cause severe performance degradation, and, depending on what type of Power System / PSeries is in use ... could potentially exhaust the DMA resources of the PCI Bus.

 

max_xfer_size should only be increased if/when AIX L2 or L3 performance support had indicated there is a need for increased values.