FreeĪs the name implies, this is a block of pages that is immediately available for usage. You may see that the VMs have CPU performance while cluster CPU utilization is lower than cluster memory utilization. To prove it, check the performance counters for each cluster. For ESXi, a common misperception is “we are short on RAM, but fine on CPU”, when it is actually the other way around. Linux and VMkernel also has its fair share of simplifying this information. Unfortunately, this is simplified in the UI.
#STANDBY VS FREE MEMORY WINDOWS#
RAM is much faster than Disk, so if you have it, why not use it? Remember when Windows XP introduced pre-fetch, and subsequently Windows SuperFetch? It’s a clue that Memory Management is a complex topic. CacheĬache is an integral part of memory management, as the more you cache, the lower your chance of hitting a cache miss. It simply went up accordingly, although again it’s fluctuating wildly. Standby Normal hardly move, but Standby Reserve took advantage of the increments. Notice the VM usable memory was increased 2x in the last 3 months.
#STANDBY VS FREE MEMORY SOFTWARE#
I think it was running Business Intelligence software Tableau. The chart above is based on >26000 samples, so there is plenty of chance for each 3 counters to fluctuate. The other 2 cache remains constantly negligible. Notice the Standby Normal fluctuates wildly, reaching as high at 90%. The following VM is a Microsoft Exchange 2013 server mailbox utility. The Standby Normal counter can be fluctuating wildly, resulting in a wide difference if it’s included in rightsizing. As a result, determining what Windows actually use is difficult.
As reported by VMware Tools, their names are:ĭifferent applications use the memory differently, resulting in different behaviour of the metrics. It’s not counted as part of Available, but counted as part of Cache. Page that was modified but no longer used, hence it’s available for other usage but requires to be saved to disk first. In use = Total - (Modified + Standby + Free Modified We know this as the amount is too high to sustain for 60 seconds if they are truly active, let alone for hours. It’s sustaining for the entire 60 seconds. This is a different behaviour to ESXi, which do not compress unless it’s running low on Free. Windows compresses its in-use RAM, even though it has plenty of Free RAM available (8.9 GB available).
If you notice on the preceding screenshot, it has compressed 457 MB of the 6.8 GB In Use pages, indicating they are not actively used. This is often thought as the minimum that Windows needs to operate. This is the main counter used by Windows, as it’s featured prominently in Task Manager. In addition to the above, it shows Transition and Zeroed. The following shows what it looks like in LinuxĪ popular tool for Windows monitoring is SysInternal. VMware Tools provide a set of universal metrics from these two popular types of Guest OSes. Windows and Linux manage memory differently, and they also name their metrics differently. It is easier to visualize it, so here it is:
Immediately means Windows does not need to copy the existing page before it can be reused.
It is the amount of physical memory immediately available for use. Mark Russinovich, cofounder of Winternals software, explains the situation in this TechNet post.Īvailable means exactly what the word means. Like what Ed has experienced, there is conflicting information, including the ones from Microsoft. Ed Bott sums it this article by saying “Windows memory management is rocket science”. Windows memory management is not something that is well explained.
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