You should consider using the XIP2 overlay file system in a DCSS for /usr executables - avoid the i/o altogether. Every linux machine shares one "memory" copy. The segment will either be in memory or paging DASD - all goodness. David
-----Original Message----- From: Linux on 390 Port on behalf of James Melin Sent: Wed 4/6/2005 11:20 AM To: LINUX-390@VM.MARIST.EDU Subject: Re: Latest on PAV's? Preventative 'what if' thinking mostly. If I share out /usr amongst guests, the disk that it is on is x many times more likely to have I/O. As x becomes a larger number, that I/O increases. At some point it will become excessive I/O for a single device path and you will see a performance hit. PAV in that situation would give guests several routes to the target data, which is what it was created to do. One could LVM a few minidisks on several devices would also solve that issue to some degree, but I've not had to implement LVM so far and I don't know what I want to for just this future issue. Unlike a lot of folken, we're not using Linux for DB2/Oracle or any heavy MySQL stuff, so LVM has not been an issue. We're grabbing our legacy data via Hipersockets to Shadow Direct into DB2. Robert J Brenneman <[EMAIL PROTECTED] To om> LINUX-390@VM.MARIST.EDU Sent by: Linux on cc 390 Port <[EMAIL PROTECTED] Subject IST.EDU> Re: Latest on PAV's? 04/06/2005 09:55 AM Please respond to Linux on 390 Port <[EMAIL PROTECTED] IST.EDU> No - PAV would not really help you in a DASD sharing environment. If you are seeing high device contention for a shared /usr volume you could create multiple volumes to spread that load across if you're using dedicated volumes. MDC on a fullpack ( or 1-end mini) could also help here by avoiding the I/O altogether. I have not seen an environment where a shared ro /usr gets that much activity though. Is this preventative planning or a problem in your current environment? Jay Brenneman James Melin <[EMAIL PROTECTED]> Sent by: Linux on 390 Port <LINUX-390@VM.MARIST.EDU> 06/04/2005 10:26 Please respond to Linux on 390 Port To LINUX-390@VM.MARIST.EDU cc Subject Re: Latest on PAV's? So LVM integration of PAV devices would not be a good way to do shared dasd amongst many guests, such as sharing /usr read only. My understanding is that Dedicate locks the device to one guest and one guest only. I guess I should have been clearer that this was my end-goal. Shared dasd using PAV. I guess that would be a good reason to supply a pav mini-disk requirement to IBM for VM enhancement. Robert J Brenneman <[EMAIL PROTECTED] To om> LINUX-390@VM.MARIST.EDU Sent by: Linux on cc 390 Port <[EMAIL PROTECTED] Subject IST.EDU> Re: Latest on PAV's? 04/06/2005 09:18 AM Please respond to Linux on 390 Port <[EMAIL PROTECTED] IST.EDU> for example: Suppose you want to have PAVs to one 3390-9 volume for the /home directory. There is the one base address ( 3000 ) and three aliases ( 30FF, 30FE, 30FD ) In the user directory, dedicate all 4 devices to the linux guest: DEDICATE 3000 3000 DEDICATE 30FF 30FF DEDICATE 30FE 30FE DEDICATE 30FD 30FD In the linux guest, make sure all the devices come up at boot time by adding them to the dasd= parameter in zipl.conf ( or whatever the preferred method is for your distro) Each device will appear to linux as a seperate entry in /dev so it may end up looking something like this: device 3000 is /dev/dasdb device 30FF is /dev/dasdc device 30FE is /dev/dasdd device 30FD is /dev/dasde If youre using SLES-8, add /dev/dasdb1 as a pv, create a vg, and then a lv on it, then reboot. The LVM startup will see the other 3 /dev nodes as extra paths to the same backing device and you can then use the pvpath command to enable the PAVs. If youre using RHEL-3 or RHEL-4 create a multipath software raid device on the 4 /dev nodes. The multipath software raid tool will know how to use 4 /dev nodes to access one device. If youre using SLES-9, I think EVMS will do multipath for you, but I'd have to get back to you with exactly how that would work. When using PAV, VM does nothing for you since you have to dedicate the devices to the guest. It stays out of the way completely. Jay Brenneman Linux Test and Integration Center T/L: 295 - 7745 Extern: 845 - 435 - 7745 [EMAIL PROTECTED] James Melin <[EMAIL PROTECTED]> Sent by: Linux on 390 Port <LINUX-390@VM.MARIST.EDU> 06/04/2005 09:36 Please respond to Linux on 390 Port To LINUX-390@VM.MARIST.EDU cc Subject Re: Latest on PAV's? I presume then, that if a PAV device is dedicated to a linux guest then the LVM of all the PAVS is still what you do from linux? Or does VM parallelize the I/O for you, being that it is handling the I/O? ---- snip for brevity ----- ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390