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Disk Arrays
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Max disk devices ?

Darren Chambers_1
Occasional Contributor

Max disk devices ?

Hello all, At present I've been tasked with connecting multiple storage arrays to multiple hosts. The storage arrays are already in use & so are already advertising disks. One of our hosts can see 980+ devices. My worry is that there is a maximum number of devices HP-UX can see. If this is exceeded, what happens ? Box crash ? Invisible disks ? Please Help, Darren Chambers
Ted Ellis_2
Honored Contributor

Re: Max disk devices ?

it really depends on how the devices are grouped... if you have enough different paths to support all the devices, then here are some system values that are pertinent...

The minor number for the group file should be unique among all the volume groups. It has the format 0xNN0000, where NN ranges from 00 to 09. The maximum value of NN is controlled by the kernel tunable parameter, maxvgs.

Now each volume group can be configured with up to 255 physical devices, which would be either single disks or LUNs from storage arrays. I think you are not in jeapardy of reaching any limits... just do some research on building volume groups to make sure you configure them in such a way to allow for using the disks/LUNs... seeing the disks is really a case of having enough mapping information to see each of them as a different entity...

check man pages for vgcreate and lvm... hope that helps
Vincent Fleming
Honored Contributor

Re: Max disk devices ?

There is a practical limit to the number of devices on HP-UX. It's not set in stone, but when you are seeing 980+ devices, expect HP-UX to start getting slow accessing them. ioscans take forever, for example. Also, in the kernel, if it needs to find a particular device, it will take longer to locate.

My suggestion - don't let all the systems see all the devices. Use Secure Manager, or it's equivelent on your disk array.

There's another reason for this besides performance - human error.

It's an all-too-common error that one admin thinks a LUN is free, and adds it to a volume group and creates a filesystem on it - just to find out (seconds later) that they just overwrote a database!!!!

Good luck!
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