Just a quick note. To quiet an alarm on a controller just run the following command:
# omconfig storage controller action=quietalarm controller=<controller id>
Use this command to disable alarms all together:
# omconfig storage controller action=disablealarm controller=<controller id>
The error “Fatal error: Can’t open and lock privilege tables: Table ‘mysql.servers’ doesn’t exist” is caused by some incomplete privilege tables. Please run the following command at a command prompt:
# cd "Program FilesMySQLMySQL Server 5.2scripts\"
# mysql --force -uroot -p mysql < mysql_fix_privilege_tables.sql
This did the trick for me – not too sure why this wasn’t part of the install but all is well now.
Most of us are familiar with RPM packages and how to install them. Sometimes it can be useful to extract the files without installing them into the RPM database. We use CPIO (a utility to copy files to and from archives) and a tool called rpm2cpio.
- Download/obtain the RPM you wish to extract.
- Make a temporary directory for your RPM extraction.
- Run the following command:
rpm2cpio wget-1.9.1-22.i386.rpm | cpio -idmv
- Your files are now extracted (with directory structure) in your temporary directory. The cpio flags are as follows:
i – restore archive
d – create any leading directories if needed
m – retain file modification times
v – verbose mode (display progress and folder structure)
Here’s what we see on the screen when performing the above operations:
While working with Linux many of us have noticed the Linux "Load Average" but never really put much thought into how this number is generated. Load averages are generated using many different metrics, disk load, CPU usage, memory usage and much more. The load average number is the total number of processes waiting in the run queue.
Using "top" provides insight into the system’s general health status.
The top command provides a view of the following main health statistics:
- Uptime (including days, hours and minutes, the user count and current time and load average)
- The total number of processes along with the number of running processes and sleeping processes
- Memory usage including total memory, used and free memory
- Swap memory usage (useful for troubleshooting slow systems)
The top command looks like this:
The topmost process on the top process list is the process using the highest percentage of CPU. The top command is available on most Unix and Linux variants.
As we’ll learn, CPU usage is not directly related to load average. Load average is an overall view of the system.
The load average rule of thumb
One quick rule of thumb I try to use (to make sure systems do not see any latency … e.g. slow processes, slow page loads, slow queries etc…) is to keep the number of waiting processes in the run queue (the load average represents total number of processes that had to wait for resources in the last 1, 5 and 15 minutes) under the total number of processors in the machine.
To check the number of processors (recognized by the Unix/Linux OS) run the following command:
cat /proc/cpuinfo | grep "processor" | wc -l
Keep in mind this command will return the total number of recognized processors. If you have a hyper-threaded P4 you’ll see two processors when really you only have one core. The same rule applies with the load average rule of thumb.
Keeping the load average under the total processor count will make for a happy, healthy and fast-responding system.
Strange enough I found a server today which had permissions set incorrectly for “/dev/null”
Here’s a fix:
ls -l /dev/null
You should see this if everything is correctly
crw-rw-rw- 1 root root 1, 3
If you get a different set of permissions like
-rw-r–r– 1 root root 1, 3
then you should (as root) delete the /dev/null with:
and recreate it (as root) again with:
mknod -m 0666 /dev/null c 1 3
Time Warner Cable traditionally used a completely coaxial network to allow subscribers to view television channels. This cable system is also a type of network. A network is simply an interconnected system of things; in our case, televisions.
There are a wide variety of networks in use today. The most basic network, the bus, connects each node (e.g. workstation) to a common backbone. Time Warner’s old network was completely a bus network, now it is only cable to each neighborhood. Most bus networks are very unreliable because if the backbone is broken at any point the entire network fails.
Figure 1 – TWC Coaxial Bus network after leaving node
As channel availability increased and cable services broadened the cable system had to be redesigned. Time Warner chose a Hybrid Fiber Coax system (HFC) to provide the adequate bandwidth and scalability that they needed and will need in the future. The company chose high-speed optical fiber to connect each of their hubs and nodes. To connect the customers to the nodes and hubs they used regular coaxial cable.
Time Warner’s fiber network is a Synchronous Optical Fiber Network (SONET) ring. This network is fully redundant. It uses fiber above and below ground to provide diverse-route connections. This type of network is not only stable, but very fast. If someone were to break one of the fiber routes, the system automatically re-routes traffic to the diverse route.
For scalability, Time Warner has ninety-six count fiber in place. This allows them to run many networks within one fiber sheath. Each service requires 4 fibers, two to carry traffic clockwise around the ring, two to carry traffic counter-clockwise around the ring and a matching set of fibers to carry the diverse path (underground or overhead) traffic. They currently run services such as Video On Demand (VOD), cable TV and high-speed cable internet.
The signals are transported on single-mode fiber (for long-haul applications) from hub to hub. At the end of each multi-mode fiber (short-distance applications) run there is an optical to electrical converter that converts the fiber to coaxial cable. The coaxial lines have to be amplified when the signal is too weak to receive on the other end. Each time the signal is amplified, there is more noise introduced to the line. Time Warner keeps their cable network no deeper than six amplifiers to keep noise to a minumum. Fiber has the same issue but the amplifiers are regenerators which are called Iridium-Doped (the technology that the amplifiers use) Amplifiers which are very expensive.
The Time Warner network is a MAN (Metro Area Network) which is a network that connects an entire city. The entire Time Warner network consists of many different MAN’s. There are other locations such as Milwaukee and Tennessee that are linked together to form a WAN (Wide Area Network.)
Figure 2 – SDTV Channel
To fit all the data onto one single coaxial cable TWC uses multiple signaling methods and multiplexing. The coaxial cable network uses FDM (Frequency Division Multiplexing) to divide the available bandwidth into “chunks” of space for each television channel, data channel or high definition digital channel. The coaxial spectrum has a bandwidth of 750MHz. Each channel of SDTV (standard definition television) occupies 6MHz of bandwidth (see figure 2.) The coax contains a sub-band from 0-55MHz which contains return traffic and is divided into 1.5MHz “chunks”. Usable bandwidth on the cable spectrum starts at 55MHz. From 55MHz to 550MHz is where all the analog signaling exists. The space from 550MHz to 750MHz is all digital data using the digital to analog signaling method 256 QAM (256 bits per baud Quadrature Amplitude Modulation.) QAM is a combination of two simpler encoding methods called ASK (Amplitude Shift Keying) and PSK (Phase Shift Keying.) In ASK the amplitude of a signal is varied to transmit data. In PSK the signal phase is varied by each bit or group of bits.
Digital Channels can achieve ten channels in the same 6MHz space as one SDTV chunk. They use MPEG2 compression to compress the video and then 256 QAM signaling to deliver the information to the viewer.
Figure 3 – Capture of a video from paramount
One main service that requires a very elaborate process to provide to customers is VOD (Video On Demand.) This service requires TWC to receive a signal from the “pitcher” or the satellite at a 3.7 to 4.2GHz C-Band transmission. The catcher receives the movie then sends the movie to the short stop which buffers the movie until it is received. The movie is then sent to the Asset Management System (AMS) which determines the validity of the movie, size and other details. Then, when the time is right, it sends the movie out to the propagation server which then sends the movie to each of the SeaChange servers located in nine of twenty hub sites.
Figure 4 – Propagation of a movie
A SeaChange server is basically a large storage center for movies that allows the movie to be delivered to a VOD customer requesting a movie. The request is sent from your cable box through the return band on your coax back through a series of checks for account payment and permission to request the movie. The movie is then sent back to you on your own personal “chunk” of a 256 QAM signal and then appears on your television.
Time Warner Cable uses a wide variety of technology to deliver the best in entertainment and maximize productivity. Their extensive use of a HFC (Hybrid Fiber Coax) network is very efficient and robust. All of this is possible because of the fundamentals of Data Communication, signaling methods, multiplexing, and networks.
The entire Time Warner network (In Kansas City)
Video On Demand
The Cable Spectrum
I’ve been seeing a lot of strange size reports on some Linux machines… specifically 64-bit systems.
The reason why you see a 1.2TB file full of null info is because the “nfsnobody” user is created with a userid of “-1″ which is the highest UID available. On a 32-bit system this is “65534″ but on a 64-bit system it’s a staggering “4294967294″. Lastlog pre-allocates space for every uid it obeys and counts 4.2 billion users just to accommodate for the user “nfsnobody”. It really doesn’t use _that_ much space but most backup utilities (E.G. EMC Retrospect) don’t know how to handle null/sparse files it will hang almost indefinitely when it tries to backup that file. Here’s the quick and dirty solution:
# usermod -u 65533 nfsnobody
# groupmod -g 65533 nfsnobody
# echo "" > lastlog
A while back I faced a difficult issue concerning a full partition that needed to be expanded – logical volume management was in use but there was no extra physical disk space to be partitioned. Here’s what I did… The solution/information below pertains to a CentOS/Redhack EL box. Release 4 or higher. BACK UP YOUR DATA!
Real World Problem:
Server "foo" has 50KB free on /home and has no additional disks to grow to. This server has all slots full and is running RAID5.
Real World Solution:
Copy the partition to another new disk (or disk array) pop into cfdisk, create a new partition on the extra free space, grow the logical volume. Resize with ext2online. Here’s a step-by-step:
- Use DD or whatever disk imaging to copy the disk to the new disk
- Boot from the new disk
- Download the CFDisk RPM
- Download ncurses-4 and ncurses-5
- Install above mentioned RPM’s
(rpm -ivh cfdisk-glibc-0.8g-1.i386.rpm; rpm –force -ivh ncurses4-5.0-12.i386.rpm; rpm –force -ivh ncurses-devel-5.4-13.i386.rpm)
- Run cfdisk /dev/device (probably /dev/sda or sdb .. you should know the device!)
- Create new partition and write changes – reboot.
- Create pv (pvcreate /dev/sda6) this creates the pv on sda6
- Add pv to volume group (vgextend VolGroup00 /dev/sda6) this
- vgdisplay will show volume group’s total size, now we can extend our lv
- Unmount the mount being used (in our case it was /home) umount /home
- lvextend -L+100GB /dev/mapper/VolGroup00/LogVol00-Home – This extends the current lv by 100GB
- Mount the partition back to it’s mountpoint (as specified in fstab) mount /home
- Use ext2online to grow the partition to it’s full size – yes, while it’s mounted! (ext2online /home &)
"df -h" will show the partition growing before your eyes!
- Enjoy a cool beverage.
The reason for using CFDisk and not FDISK is because fdisk will not recognize the disk size change because DD copies everything – all structures – cfdisk is the only utility (at least that I found) that can resize in this type of situation.
A long time ago I performed an installation of an Oracle cluster. This cluster, unlike other real clusters, is a cluster using RedHat Cluster Suite (RHCS) and involved two Dell 1950’s each with 8GB RAM and two 146GB 15K SAS drives. Each of these machines are connected to a CLARiiON SAN via QLogic FC cards through a pair of MC Data FC switches.
This cluster is more of an active/active cluster but, unlike Oracle’s RAC clustering software, there are four instances running on one machine and four running on the other; effectively evening out the load. There are quite a few downsides to this method which I will outline below. There are, however, a few pro’s as well.
- Allows for applications not written for RAC cluster to still be used in a clustered environment for High Availability.
- Expensive! RHCS was needed for this setup and GFS ($2000 per node per year) was needed. This company chose to use a supported version of Linux, Cluster Suite and GFS. Of course, you can do this freely as the OS, File System and cluster utility are all freely available.
- Not truly load balanced. This setup was meant to be load balanced but they are still two separate Oracle installations on two machines. The clustering suite just allows for proper failover.
- RHCS (Red Hat Cluster Suite) was never made to support Oracle on both systems. Oracle’s Enterprise Manager will not start for both installations on the same Ethernet adapter. This situation would be encountered if both installations would fail over to one machine. EM is inaccessible for the databases which failed over.
- Lots and lots of editing needed to be done to make Oracle work properly – editing the startup scripts, oratab, creating more custom startup scripts and more. In general this was a messy install.
In summary, I would not recommend using Oracle with RHCS. I would highly recommend that the application be re-written to be “RAC Compatible” so that you can fully utilize the power of Oracle load-balancing. This will save time and money in the short run and possibly the long run depending on what kind of support issues we might encounter. RHCS is great but I wouldn’t recommend it to anyone for Oracle.