Featherweight Linux VNC services

Bart Sjerps General 2 Comments

This article describes how to set up a very lightweight VNC service under CentOS/Red Hat.

Virtual_Network_Computing_(logo).svg

Intro

In Red Hat Enterprise Linux (and derivates, I use CentOS) you can run a VNC service to allow graphical connections to a linux system. I was looking for a very lightweight VNC service (no fancy desktop with all the bells and whistles, just something that lets me do some stuff that requires an X session and run an Xterm – such as installing Oracle or running Swingbench, without using another host with an X client). In other words, a typical service for virtual machines that run as servers (such as database servers, web servers, etc).

CentOS standard method

I tried the standard documented way to do this in CentOS: CentOS Virtual Network Computing using the standard tigervnc-server method, but found a few issues with the way they set it up:

  • For every user requiring VNC services, you need to customize the configuration
  • If one user deletes or corrupts his VNC password file, the whole service stops working (fix via normal SSH login but requires skilled user)
  • If a user messes up his xstartup file he is locked out (fix via normal SSH login but requires skilled user)
  • Users need 2 passwords: for their (own) VNC service, and the usual one for Linux
  • Their X window and VNC processes are always running and thus eating resources even if not used
  • If their X session hangs (i.e. window manager killed, or simple logout) it’s hard or even impossible to clean up and restart (see section 4 in the mentioned article: Recovery from a logout) without resetting the whole VNC service
  • Every user requires a separate, unique TCP port

All by all, nice and easy for a small test server with a few users, but no good for larger environments. The good thing is that the desktops are persistent, i.e. you may disconnect and reconnect later and the VNC session will be as you left it. And you can install lighter desktop environments (twm or openmotif) instead of the huge and heavy Gnome desktop.

But I was looking for something better.

(more…)

Loading

Fun with Linux UDEV and ASM: Using UDEV to create ASM disk volumes

Bart Sjerps Oracle, Virtualization 34 Comments

floppy-disksBecause of the many discussions and confusion around the topic of partitioning, disk alignment and it’s brother issue, ASM disk management, hereby an explanation on how to use UDEV, and as an extra, I present a tool that manages some of this stuff for you.

The questions could be summarized as follows:

  • When do we have issues with disk alignment and why?
  • What methods are available to set alignment correctly and to verify?
  • Should we use ASMlib or are there alternatives? If so, which ones and how to manage those?

I’ve written 2 blogposts on the matter of alignment so I am not going to repeat myself on the details. The only thing you need to remember is that classic “MS-DOS” disk partitioning, by default, starts the first partition on the disk at the wrong offset (wrong in terms of optimal performance). The old partitioning scheme was invented when physical spinning rust was formatted with 63 sectors of 512 bytes per disk track each. Because you need some header information for boot block and partition table, the smart guys back then thought it was a good idea to start the first block of the first data partition on track 1 (instead of track 0). These days we have completely different physical disk geometries (and sometimes even different sector sizes, another interesting topic) but we still have the legacy of the old days.

If you’re not using an Intel X86_64 based operating system then chances are you have no alignment issues at all (the only exception I know is Solaris if you use “fdisk”, similar problem). If you use newer partition methods (GPT) then the issue is gone (but many BIOSes, boot methods and other tools cannot handle GPT). As MSDOS partitioning is limited to 2 TiB (http://en.wikipedia.org/wiki/Master_boot_record) it will probably be a thing of the past in a few years but for now we have to deal with it.

Wrong alignment causes some reads and writes to be broken in 2 pieces causing extra IOPS. I don’t have hard numbers but a long time ago I was told it could be an overhead of up to 20%. So we need to get rid of it.

ASM storage configuration

ASM does not use OS file systems or volume managers but has its own way of managing volumes and files. It “eats” block devices and these block devices need to be read/write for the user/group that runs the ASM instance, as well as the user/group that runs Oracle database processes (a public secret is that ASM is out-of-band and databases write directly to ASM data chunks). ASM does not care what the name or device numbers are of a block device, neither does it care whether it is a full disk, a partition, or some other type of device as long as it behaves as a block device under Linux (and probably other UNIX flavors). It does not need partition tables at all but writes its own disk signatures to the volumes it gets.

[ Warning: Lengthy technical content, Rated T, parental advisory required ]

(more…)

Loading

Getting the Best Oracle performance on XtremIO

Bart Sjerps Oracle, Performance No Comments

XtremIO+Stack+NB+copy
(Blog repost from Virtual Storage Zone – Thanks to @cincystorage)

UPDATE: I’ll say it again because there seems to be some confusion: THIS IS A REPOST!

Original content is from the Virtual Storage Zone blog (not mine). Just reposted here because it’s interesting and related to Oracle, performance and EMC storage. Enjoy…

XtremIO is EMC’s all-flash scale out storage array designed to delivery the full performance of flash. The array is designed for 4k random I/O, low latency, inline data reduction, and even distribution of data blocks.  This even distribution of data blocks leads to maximum performance and minimal flash wear.  You can find all sorts of information on the architecture of the array, but I haven’t seen much talking about archive maximum performance from an Oracle database on XtremIO.

The nature of XtremIO ensures that’s any Oracle workload (OLTP, DSS, or Hybrid) will have high performance and low latency, however we can maximize performance with some configuration options.  Most of what I’ll be talking about is around RAC and ASM on Redhat Linux 6.x in a Fiber Channel Storage Area Network.

Read the full blogpost here.

 

Loading

Oracle, VMware and sub-server partitioning

Bart Sjerps Oracle, Virtualization 9 Comments

costsaveLast week (during EMC world) a discussion came up on Twitter around Oracle licensing and whether Oracle would support CPU affinity as a way to license subsets of a physical server these days.

Unfortunately, the answer is NO (that is, if you run any other hypervisor than Oracle’s own Oracle VM). Enough has been said on this being anti-competitive and obviously another way for Oracle to lock in customers to their own stack. But keeping my promise, here’s the blogpost 😉

A good writeup on that can be found here: Oracle’s reaction on the licensing discussion
And see Oracle’s own statement on this: Oracle Partitioning Policy

So let’s accept the situation and see if we can find smarter ways to run Oracle on a smaller license footprint – without having to use an inferior hypervisor from a vendor who isn’t likely to help you use it to reduce license cost savings…

The vast majority of enterprise customers run Oracle based on CPU licensing (actually, licensing is based on how many cores you have that run Oracle or have Oracle installed).
(more…)

Loading