Whilst I’m a fan of using percentages for my disk space checks, sometimes an explicit size is more appropriate. So, you’d expect the following to work nicely:

$USER1$/check_disk -w 5G -c 1G -p /data/foo

If you don’t actually test that this works (by artificially filling your disk and seeing what happens), you may be dismayed to find that you only get alerted when the disk has 5MB of free disk space. Why is this?

Because Nagios, despite the fact that nobody has sweated the megabytes for about a gazillion years, doesn’t support ‘G’ as a suffix for thresholds. Oh, it’ll make a good show of pretending — after all, the output formatting options have ‘GB’ as an option — but nope, for your thresholds it’s “5000M” all the way.

ROCK ON!

This is the output of iptables -L on a webmin-managed box I just saw:

Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere
ACCEPT     all  --  anywhere             anywhere
ACCEPT     tcp  --  anywhere             anywhere            tcp flags:ACK/ACK
ACCEPT     all  --  anywhere             anywhere            state ESTABLISHED
ACCEPT     all  --  anywhere             anywhere            state RELATED
ACCEPT     udp  --  anywhere             anywhere            udp spt:domain dpts:1024:65535
ACCEPT     icmp --  anywhere             anywhere            icmp any
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:smtp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:domain
ACCEPT     udp  --  anywhere             anywhere            udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:http
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:pop3
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:imap
ACCEPT     udp  --  anywhere             anywhere            udp dpt:imap
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:https
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:mysql
ACCEPT     tcp  --  anywhere             anywhere            tcp spt:mysql
ACCEPT     tcp  --  anywhere             anywhere            tcp dpts:terabase:samsung-unidex
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ndmp
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:dnp
LOG        all  --  anywhere             anywhere            LOG level debug prefix `DROPPED = '
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:ftp-data 

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     tcp  --  anywhere             anywhere            tcp spt:ftp-data dpt:ftp-data
ACCEPT     tcp  --  anywhere             anywhere            tcp spt:ftp dpt:ftp

Lovely that it has all those ports and whatnot opened up, but what’s with the ACCEPT policies?

Webmin: Now with FAILWALL management!

I should have been in marketing.

And this is why we co-locate in Globalswitch, a top-tier facility with floors that AREN’T MADE OF BALSA WOOD.

Racks are pretty heavy, sure, but they totally wtfpwned those tables there

In an ideal world every service would support High Availability and Load Balancing, would scale up easily and cleanly and all of us systems administrators would be paid bucketloads to play golf all day while the computers did all the hard work. To quote Dylan Moran of Black Books fame, “Don’t make me laugh…bitterly”.

I’ll cut to the chase – sometimes you have to really shoehorn technologies to do what you want. Fortunately I love doing this, and the technologies of today’s article are virtualised Windows 2008 on Xen, and Oracle XE 10g. Neither likes to play ball, for a few reasons:

• Generally speaking, when you virtualise an OS you want to have para-virtualisation drivers enhancing the hardware support. Open Source Xen has PV drivers, but they are not signed with a legitimate certificate. Windows 2008 does not play nicely with unsigned or test-cert-signed drivers.
• Oracle is just a messy, messy, nasty thing. Yes, paid versions undoubtedly support all manner of loadbalancing and HA options, but the free one does not.

Adding HA to Windows 2008 on Xen

The basic procedure was as follows:

• Install the telnet server within Windows (making sure to lock it down in the firewall to only be accessible by the host machines)
• Create a special admin account and password used for triggering a shutdown
• Create an Expect script which logs into the VM via telnet, and issues the shutdown command
• Create a modified version of the Heartbeat Xen resource agent which calls the expect script to shut down the VM (and wait a safe period of time) before “xm shutdown” is called. Without this, “xm shutdown” will simply power off the VM (in absence of working PV drivers).

The VM was already running on a DRBD volume between the two HA Xen servers, so I was able to just create a standard set of Heartbeat resources to control DRBD primary/secondary mode and the startup/shutdown of the HA WIndows VM. For your benefit (if you want to recreate it) here is the expect script:

#!/usr/bin/expect -f
#
# Script which "automates" shutting down a Windows VM

# Don't log telnet output and commands to stdout, and set a reasonable timeout.
log_user 0
set timeout 3

# Log in via telnet and issue commands. Fairly straightforward.
spawn -noecho /usr/bin/telnet 192.168.1.1
sleep 0.5

# login as the "shutdown" user
expect {
 -re "login: $" {send "shutdown\r"}
 timeout exit
}
sleep 0.5
expect {
 -re "password: $" {send "mysecretpassword\r"}
 timeout exit
}
sleep 0.5
expect {
 -re ">$" {send "shutdown /s /t 0\r"}
 timeout exit
}
sleep 0.1
expect {
 -re ">$" {send "exit\r"}
 timeout exit
}
exit

The rest is fairly self-explanatory if you understand Heartbeat.

Oracle XE 10g

This was more of a learning process, since usually you just install Oracle and leave it the hell alone. Not so for me.

• Install Oracle on both nodes using (fortunately) the RPMs they provide
• Configure Oracle on both nodes including creating the databases, using the same password for SYSDBA
• Shutdown both instances of Oracle
• Create the DRBD resource, and mount it on the primary node
• On the primary node, move the contents of /usr/lib/oracle/xe/oradata and /usr/lib/oracle/xe/app/oracle/flash_recovery_area onto the mounted DRBD
• On the secondary node, delete the aforementioned paths
• Bind mount the oradata and flash recovery area from the mounted DRBD volume into the correct places in the directory tree.
• Start Oracle

After I had created a Heartbeat resource group which contained the DRBD resource, the DRBD filesystem mount, the aforementioned bind mounts and the Oracle service itself I was quite pleased to see that Oracle plays quite nicely with our shoehorned HA setup. You’ll want to make sure you have a properly fixed Oracle init script though, as the supplied one is fairly bad.

After making Oracle and Windows 2008 work nicely in HA, I’m almost certain any service no matter how bad can be shoehorned in a similar way to give you decent availability even when it was n’t originally intended.

I kid you not, we just received this in a piece of marketing guff from our favourite enterprise vendor.

“Industry analysts predict that Linux and Windows will soon dominate the operating system space. How you respond to this is critical.”

Meanwhile, industry analysts predict that more than 98% of the population will be consuming oxygen by 2010.

I’ve written recently on how to handle systems with very large storage subsystems. One would think that as we make our way through 2009 that the supporting tools for such large filesystems are at the top of their game, but as I’ve been playing with 24TB of storage I’ve realised that this is hardly the case:

• The most commonly used bootloader for Linux systems, GRUB, doesn’t yet have capabilities to boot from GPT partitions (at least not in the stable release)
• The most commonly used partitioner, fdisk, doesn’t support GPT-partitioned disks (and hence no disk larger than 2TB)
• GNU parted, which does support GPT, insists on performing all partition resize operations itself (including resizing the contained filesystem). Since it doesn’t yet understand LVM, it can’t resize any partition that contains an LVM PV.

Today I ran into what appears to be a bug in the CentOS 5.3 installation partitioner, which left my 12TB RAID volume only partitioned to 8TB when I had supplied the –grow parameter in the Kickstart script. Since parted can’t resize LVM partitions, and there don’t appear to be any other tools out there at the moment for GPT partitioning on Linux, I’m left in a less than ideal position.

GNU parted can’t resize the partition because it can’t understand LVM. Fortunately I can just use it to create another partition with the remaining space and add it to the existing LVM volume group but this is really just a hack, and one that disturbs my obsessive-compulsive sysadmin nature. Were it not for the flexibility of LVM, we would be in a bit of a mess.

Sadly, it seems the large filesystem support that will soon become essential for everyone is largely lacking in adequate support.

Anyone in the sysadmin or developer worlds will know many examples of flagrant violations of standards in the IT world. Some are perpetrated by our coworkers, but a surprisingly high amount are perpetrated by vendors. Not all of them are by Microsoft, either!

One big win for systems administration at Anchor is our use of APC Rack Power Distribution Units. These have been documented elsewhere in our blog and wiki but suffice it to say that having remote control over your power ports is a Very Good Thing. Situations where you have servers or other devices with multiple power supply units complicates things slightly, but not that much, especially with the aforementioned Rack PDUs in place.

APCs in particular allow you to configure what are called Multicast Groups. Essentially you tell a couple of the Rack PDUs to talk to each other and share information, and WHAMMO you can turn off and turn on a bunch of ports on separate Rack PDUs simultaneously! So rather than turning off the power to one PSU then rebooting the other, you can conduct a reboot of the power to both PDUs with a single command.

The confusion comes during the configuration of the Multicast Group option. Multicast is a very under-utilised feature of IPv4 (which has now partially been rectified in IPv6), in fact a large chunk of the IPv4 address space is allocated to multicast (and is technically called the Class D space). As with all other portions of IP address-space, this has been carefully portioned into sections and allocated to various purposes. You can see the full list here:

http://www.iana.org/assignments/multicast-addresses/

Being a good sysadmin I consider standards to be of paramount importance, so naturally I wanted to configure our Rack PDUs with multicast addresses suitable for the purpose. There are many existing references on the Internet for how to pick sane and standards-obeying addresses from the multicast range. However, when attempting to follow standards and good reason, I was confronted with this error message:

Multicast IP Address is out of range. Valid values are 224.0.0.3 - 224.0.0.254.

Uh, what? I was under the impression that the range 224.0.0.0/24 was already heavily allocated to entities and purposes other than APC Rack PDUs! So much for following the standard, APC.

Every now and then we see an example of application failure so astounding it literally brings tears to our eyes. We have a client whose legacy application is unfortunately still running on an ancient version of Oracle Weblogic and which must be maintained until the new, flashy .NET version of their site is complete.

We were alerted this morning to a problem with some of the Weblogic content – the pages were timing out. Diagnostics were fairly fruitless – packet captures showed nothing useful, and the logging from Weblogic left much to be desired. We started considering more outlandish possibilities such as I/O load causing issues, recently applied updates and so on. Even rebooting was considered (given it is running on Windows).

The first clue of note was the open file list from the Weblogic processes – one such example stood out:

C:\weblogic\state\Sa0V\b1gR\O1Ok\WqYN\9kiv\IQT2\SHGx\C3ri\aE1z\L1YH\X5QW\
gdkB\B2PB\pPPw\uHDK\p1a7\I0l5\94sU\kQ43\+533\5517\5738\7484\6253\_-10\
6273\1519\_6_8\888_\8888\_700\2_702_8\888_

For the sake of your screen, I have manually wrapped this Godzilla-like filename.

Perhaps you are familiar with file bucketing already, but if not, typically the directory structure used will have a relatively sane scheme for locating files and only extend a few levels deep. What we saw in this instance was a completely new breed of monster. Admittedly the absolute path of this file is less than 200 characters out of a limit of more than 32,000 but the naming strategy and depth of the structure has us flummoxed.

But this was only the tip of the proverbial iceberg. When we requested Windows to show us the properties of this state folder it took over an hour to completely calculate the file and folder totals, and the result is impressive:

Web logic makes efficient use of the filesystem

Yes you read that right – over 10 million nested directories. By this stage we had already moved the state directory out of the way and created a new one, and restarted Weblogic. It seemed happy and quite responsive after that. My suspicion is that someone developing this application at some point ran into a limitation with their filebucketing algorithm, and resolved to solve the problem once and for all, evidently by making it possible to efficiently filebucket every file in the known universe.

It’s no secret that we’d rather be working on Linux than Windows here at Anchor. It is, by and large, much more annoying to actually get anything done, but it also just breaks in opaque and unexplained ways. O Windowes, let me count the ways in which you are broken! This is one such problem we ran into yesterday.

Hard drive failure is a fact of life when you run servers, by sheer virtue of that fact that you have hundreds of them. To mitigate the risk and reduce unscheduled downtime, we use Window’s built-in software RAID feature. It’s not an enterprise solution, but it gets the job done. What’s important is staying online and not losing data.

Did I mention that trying to monitor a Windows box is a nightmare? A colleague of mine wrote a script to allow us to keep a watchful eye on Windows RAID volumes, it’s a lifesaver. A recently-deployed machine got a broken mirror, which we were able to act on immediately. We removed the dodgy mirror and prepared a replacement (we always have plenty of spares, of course). Allow me now to re-enact this scene…

Windows (sounding almost efficient): The driver has detected that device \Device\Harddisk1\DR9 has predicted that it will fail

Sysadmin: Thanks, Windows, I’ll get right on that. You didn’t say whether that was SMART, or just voodoo, but whatever, it’s good to know.

The bad drive is removed and a replacement installed in the hotswap drive bay

Sysadmin: Okay, Windows, do your stuff. “Scan for new hardware”, please.

A pause.

Sysadmin: Ahem, Windows, “Scan for new hardware” and find my drive.

Windows: ‘Ey there, chaps. Do what now, you say? AIEEEEGRH!!

The server stops responding entirely, necessitating a touch of the reset button

Needless to say, we’re rather unimpressed, and have to call the customer to let them know why it’s just dropped offline.

A quick check of the logs is in order. It’s also frustrating that there’s no sane way to scroll through log entries in Windows with something like a text editor, or to “tail” a log as it’s updated in realtime.

09:36 – The previous system shutdown at 9:21:23 AM on 8/10/2008 was unexpected.

Okay, it went down at 09:21, which is correct. Now if we look back in time a little…

09:21 – dmio: Harddisk1 write error at block 1953524618 due to disk removal

*sigh* And this is after the disk was removed cleanly…