Information Technology Reference
In-Depth Information
Web: 100 shares
Database: 200 shares
App 1: 200 shares
App 2: 250 shares
Figure 1.5
Using FSS to Ensure Minimum CPU Portions
Insufficient memory can cause more significant performance problems than
insufficient CPU capacity. If a workload needs 10% more CPU time than it is
currently getting, it will run 10% more slowly than expected. By comparison,
if a program needs 10% more RAM than it is currently getting, it will cause
excessive paging. Such paging to the swap disk can decrease workload perfor-
mance by an order of magnitude or more.
Excessive memory use by one VE may starve other VEs of memory. If
multiple VEs begin paging, the detrimental effects on performance can be
further exacerbated by various factors:
■
A shared I/O channel can be a bottleneck.
■
If VEs share swap space, fragmentation of the swap space can cause exces-
sive head-seeking within the swap area.
■
If each VE has a separate swap area but all of these areas are present on
one disk drive, the drive head will continuously seek between the two swap
areas.
If paging cannot be avoided, swap areas should be spread across multiple
drives or, if possible, placed on low-latency devices such as solid-state drives
(SSDs). However, it is usually difficult to justify the extra cost of those
devices. Instead, you should try to avoid paging by configuring sufficient
RAM for each VE.
Memory controls can be used to prevent one VE from using up so much
RAM that another VE does not have sufficient memory. The appropriate use
of memory controls should be a general practice for consolidated systems.
Inappropriate use of memory controls can cause poor performance if
applications are granted use of less RAM than the “working set” they need
■
Search WWH ::
Custom Search