Memory Errors on Modern Servers

I used to see memory degrading on Cisco UCS blades. But less see on HPE blades. I thought it maybe quality control problem of Cisco manufacture. Today I read two articles in Cisco website, it explains why we see memory degrading and how it works. I attached the articles below.

Managing Correctable Memory Errors on Cisco UCS Servers

UCS Enhanced Memory Error Management

The conduction in the whitepaper is not only specific for Cisco UCS, but also for any modern servers. Following is summary of why memory errors rates is going high nowadays.

Larger memory systems contain more bits
Higher capacity DRAM chips require smaller bit cells which result in fewer stored charges per bit
Lower operating voltages can lead to reduced noise margin
Higher operating speeds can lead to reduced timing margin

Oracle Utilizes 50% of Physical Processors on HPE Server

DBA team told me Oracle was running slow on a HPE server. I observed the CPU utilization was about 50% of overall capacity. Whenever Oracle database bumps up the system experienced slowness.

Further digged into the issue, I see Oracle workload only ran on single physical processor, but the server has two processors. And the Windows 2012 R2 resource manager show the system used Processor Group, the two physical processors were grouped out. This technology is described in Microsoft MSDN article.

To fix the issue you have to change value of “NUMA Group Size Optimization” to “Flat” in BIOS. Please refer to HPE article for detail steps.

Detail of HPE server behavior is documented here. Please note, the article says it impacts to ProLiant Gen9 and Intel E5-26xx v3 processors. But it actually also impacts to Intel E5-26xx v4 and Synergy blades.

虚拟主机无法获得DHCP IP地址

刚解决了一个问题，快速更新一下。当虚拟主机无法获得DHCP IP地址时，应该做的第一件事情是检查防火墙，无论是Windows防火墙或者物理防火墙。UDP端口67和68不能被阻挡掉。否则会出现虚拟主机只能获得169.x.x.x的IP地址，这个地址是不可用的，表示虚拟主机无法从DHCP服务器获得地址。

这两个端口是DHCP客户端用来从DHCP服务器获取IP地址的。具体的技术细节可以参考RFC文档。

DHCP uses UDP as its transport protocol. DHCP messages from a client

to a server are sent to the ‘DHCP server’ port (67), and DHCP

messages from a server to a client are sent to the ‘DHCP client’ port

(68). A server with multiple network address (e.g., a multi-homed

host) MAY use any of its network addresses in outgoing DHCP messages.

我在排错过程中也用到了这篇文章。

搜索虚拟主机时提示：Login To The Query Service Failed

使用vSphere Client登录vCenter Server 6.0时可能会出现如下报错信息：

Login to the query service failed.

The server could not interpret the communication from the client. (The remote server returned an error: (500) Internal Server Error.)

这是因为在登录vSphere Client时勾选了”Use Windows session credentials“。试试取消它。