Re: Expanded Storage

[Edward M. Martin]

Hello Everyone,         I am very light on the XSTORE versus Main.   Where is the best place to read And understand?   Ed Martin Aultman Health Foundation 330-588-4723 [EMAIL PROTECTED] ext. 40441 From: VM/ESA and z/VM Discussions [mailto:[EMAIL PROTECTED] On Behalf Of David Boyes Sent: Friday, February 03, 2006 10:10 AM To: VMESA-L@LISTSERV.UARK.EDU Subject: Re: Expanded Storage    >  Our VM will have 4GB, only one Linux Guest with 1 or max 2GB storage, 512MB swap vdisk for this linux guest.   >  Remaining storage 512mb is for CP, some VM Users (TCP, administration users, ...) and MDC.   >  Because we almost are V=R we probably will lock the pages of the Linux Guest, so there should not   >  be any significant paging.   >  Is there any advantage if some of the storage is used as expanded storage?     A small amount of XSTORE reduces the impact of VM paging  in that VM will page to XSTORE and then to real disk. As Rob said, page locking is second-guessing CP's internal management algorithms (which often causes more problems than it solves), and having some XSTORE allows you to sustain paging rates that would cripple you otherwise. VM can also move some other functions into XSTORE (like MDC, etc) that may help you while you have a 31-bit only system.   > my colleague phones with a ibm guy who told him that - if using more than 2 gig - some expanded storage is recommended   >  (he suggested 512mb) to help vm with "internal" management.     For 4.4 systems, I generally start with at least 1G of XSTORE and tune up/down depending on the reports from Perfkit or other performance monitoring tools. Rob's comments wrt to thrashing below the 2G line are important; with virtual machine sizes as large as yours (even though you can afford to lock them in storage) you will see some amount of page motion. Depending on your workload, you may get a fair amount of benefit from MDC which can live in XSTORE, freeing main storage for other uses.   Usual advice of getting a baseline with your performance monitor, adding the XSTORE and then measuring again applies.