IBM ZVM - FOR LINUX V6 RELEASE 1, Начало работы

Страница: 43 / 172

requirement. This value can be decreased by a fraction of the real memory
available. See “Paging Space” in
z/VM: CP Planning and Administration .
v
Add paging space on a volume basis: do not use the paging volume for other
purposes.
“Steps for adding a paging, spooling, or user volume” on page 35 tells you how
to add a paging volume.
Related information
For information about how z/VM uses DASD space and DASD space calculations,
see “Direct Access Storage Requirements” in
z/VM: CP Planning and Administration ,
SC24-6178.
For the Linux file system
v
For disks for each Linux virtual server, the simplest guideline is to provide one
3390-3 at a minimum. A one-volume configuration supports many of the default
packages installed by each Linux distribution. The need for additional DASD
space depends on which additional products you install, the levels of those
products, the size of user applications associated with those products, and
end-user data.
Linux views disk space in bytes while z/VM views disk space according to the
device geometry (for example, number of cylinders). Regardless of the 3390
model, each cylinder holds approximately 670 KB when formatted. A 3390-3 has
3338 usable cylinders, which means it can hold about 2.2 GB when formatted.
The difference between 3390 models is the number of cylinders the model has. A
3390-9 has three times the capacity of a 3390-3, so it holds approximately 6.6 GB.
Consult product documentation for additional DASD space requirements. Your
Linux distributor will tell you how much disk space to use for minimum and
full installations.
v
Eliminating certain Linux packages can help reduce your DASD requirements.
Consider a minimal Linux installation to save disk space.
v
Another strategy to save DASD is to divide up the Linux file system into
read-only and read/write minidisks, then share the read-only minidisks among
the virtual machines running Linux.
v
Do not dedicate DASD to Linux (that is, do not allocate an entire DASD to
Linux for its exclusive use). Instead, use minidisks for Linux volumes, especially
those whose I/O operations are primarily read operations, to take advantage of
minidisk caching. The z/VM Control Program by default maintains a minidisk
cache for better performance. However, if there are many write operations to the
minidisk, the extra Control Program overhead used to maintain the cache
outweighs the benefits of caching. If the I/O operations include many write
operations, turn off minidisk caching for the minidisk by using the CP command
SET MDCACHE MDISK or the MINIOPT statement in the user directory.
v The Parallel Access Volume facility allows a controller to offer multiple device
numbers that resolve to the same DASD, which allows I/O to the same DASD
to happen concurrently. If you do not have the Parallel Access Volume facility,
each DASD can do only one I/O at a time. To have your Linux file system
perform well without the Parallel Access Volume facility, you can spread the file
system across separate volumes and use the Linux logical volume manager,
which maximizes the opportunity for the I/Os to the volumes to happen
concurrently. For example, you could set up two stripes so Linux can do two
I/Os at a time. Note that the volumes should be on separate controllers to avoid
contention.
Chapter 2. Planning for Linux virtual servers
29