The question of Page File sizing has come up recently a number of times and so I thought I would start off with providing some guidance that I have gathered (which is based on a couple of discussions with folks at Microsoft).
Hyper-V Parent Pagefile Config
· This is basically the same as for any other large, many GB, x64 system as per recommendations below
· Wouldn’t expect many of the components (services and worker apps) in the parent to need much pagefile space and most of the RAM is under the control of the ‘vmm’ component (to be given to guests), it is unlikely to need the pagefile to back that
· So a simple 4GB pagefile on the Windows (boot) drive should be sufficient both as a reasonable pagefile and big enough to get a kernel only dump in most situations
Pagefile notes
The informal guidance I usual give, for large 32bit and large 64bit systems, is as follows:
1. Pagefiles have two primary roles
a. as a pagefile to allow virtual memory to work better and potentially allow the server to do more work
b. for use in generating crash dumps for problem investigation
2. Size required for a) can be argued about, and even whether one is necessary at all, but in general a pagefile, or pagefiles, of several GB is recommended. Some scenarios may benefit from a pagefile of size of up to or larger than RAM size, and for best performance an additional dedicated pagefile drive could also be used.
3. Size required for b) (dumps) is usually the key factor and relates to the pagefile on the boot (i.e. Windows) drive, which may have some space constraints of its own
4. First you need to confirm if you really need Full (Complete) dumps or if default kernel only dumps are acceptable
5. In 95% of cases a kernel only dump is sufficient
a. A kernel dump on 32-bit, even in PAE mode with lots of RAM, will always be < 2GB
b. A kernel dump on x64 could theoretically be quite large (almost as large as RAM)
c. In practice is usually less than 4GB for mid range systems
d. For very high end servers they might be up to 16GB or potentially more
6. What size pagefile (on the boot/windows drive) should you have ?
a. Provided it is bigger than 16GB you should be able to catch a kernel dump in 99.5% of cases
b. And even 4GB or 8GB will be sufficient in most cases
c. Size constraints (and free space requirements) on the boot drive may be the limiting factor
d. If you really want Complete dumps, then will have to set the key in the registry (as the gui won’t allow complete dumps to be set with >2GB RAM)
e. and ensure you have a pagefile of RAM + a bit, plus sufficient free space for the dump file
7. Also note that dumping that amount of RAM causes significant down time
a. In my test a 16GB dump took approx 40 minutes (after crashing and before it could reboot)
8. Also have the logistical issue of how to get such large dumps to Microsoft
NB The way the pagefile (on the boot drive) is used for creating dumps has changed somewhat in Vista/2008 (new optional DedicatedDumpFile functionality especially useful for boot from SAN).
Regards
Patrick Lownds