Ocfs users - May 2005 - MAX_LUNS SIZE LIMIT ON RHEL 3.0 and 4.0

Dear List Users-

IHAC planning storage layout and is looking for the following MAX_LUNS 
size limit on RHEL 3.0 and 4.0. Details are below. Customer database 
size is estimated to grow to 5 TB and worries that they will not be able 
to present enough devices to the system if used with EMC powerpath and 
RHEL 3.0 max_lun limitations. I have advised on using OCFS or ASM as 
this is a 10g Database to avoid raw device limitations. In any case, 
answer to "max_luns" should appease the customer. Any info will be 
appreciated.

Please copy me on your replies to the group.

Thanks,

-sj



SERVER SUMMARY:

 
HP Itanium 2
rx4640
HBA INFO... (two different numbers for the same card)
HP PART #A6826A
QLOGIC Model #Q2342A
Dual Ported HBA (4 ports total, with 2 going to the DMX)


RESEARCH DETAIL

As per EMC PowerPath expert - PowerPath could handle any number of SCSI 
devices and that the limitation would be either an OS or an HBA driver 
limitation. 

According to RedHat - Modify /etc/modules.conf file which states 
"max_luns=".  This is normally 128, but can be changed to 256 to
support
256 SCSI devices.  Will a higher number for "max_luns" be supported on
RHEL 3 update 4 or RHEL 4?

QLOGIC - A QLOGIC engineer stated that there can only be 256 devices 
seen per HBA which follows the fibre channel standard of 256 devices per 
channel.  Because we are multipathing, that number would be cut in half 
to 128 unique devices per HBA (2 paths per actual LUN device).  Since we 
have 2 HBA's that we will be using for the DMX, we will have 128 devices 
per HBA port, or 256 total unique devices.  In short, this means that 
the OS will be are limiting factor, not the HBA.



-- 

_____________________________________

 Shankar Jayaganapathy 
 Partner Solutions Group
 Technology Business Unit
 Oracle USA Inc.
 Phone: 713.553.7942 


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