That title might be longer than this post, but if you’re running into problems with zone transfers that don’t appear to happen, check to make sure you are putting your zone files in /var/cache/bind.

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So, as these things go, I spent 2 days looking at my OpenVPN config files and bridging setup before finding the solution to my problem was elsewhere.

A little background: I created a new OpenVPN VM using the Debian Squeeze net install CD, configured it to match what was already working on a physical Windows XP box, but only had limited success. I was able to connect to the VPN, ping the OpenVPN server on the network, but couldn’t connect to anything else. Trying to ping another server from the VPN client, and running tcpdump on that other server showed that it was receiving ICMP requests and replying, but they were not making it back to the VPN client. I tried a hundred different ways of creating the bridge on the OpenVPN server, but nothing worked. Finally, good old Google found the answer. The ESXi virtual switch drops promiscous packets by default. To fix it, open the vSphere Client, click on the ESXi host on the left side, click on the “Configuration” tab on the right, click “Networking” in the Hardware box, click on “Properties…” at the top-right of your “Virtual Switch: vSwitch#” graphic. Now on the “Tools” tab of this popup window, select the “vSwitch” and click the “Edit…” button. In this popup, click on the “Security” tab and change “Promiscuous Mode” from “Reject” to “Accept”. Click “OK” then “Close” and you should be all set.

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echo "# Disable IPv6" >> /etc/sysctl.conf
echo "net.ipv6.conf.all.disable_ipv6 = 1" >> /etc/sysctl.conf
echo "#" >> /etc/sysctl.conf
reboot

Oh yeah, and if exim freaks out,
vi /etc/exim4/update-exim4.conf.conf
and change dc_local_interfaces so it reads
dc_local_interfaces='127.0.0.1'

Snapshots are available with VMware Workstation, VMware Fusion, VMware Server and ESX/ESXi.

Windows has a feature called system restore.  The idea behind System Restore is to revert to a point in history in case something goes wrong – i.e.: patch Tuesday. It’s an undo feature for your Windows OS. There is overhead for this undo feature, especially on the IO front which is generally acceptable for a dedicated desktop but not ideal for VMs.

One can approximate the function of System Restore with snapshots. Snapshots should be used only when modifying a VM, i.e. patch Tuesday, new software, etc… The idea is “I know I’m making a change so I snapshot the VM”, I execute the change, and test. Once testing reveals no issues and everything works as expected, the snapshot is removed.  (Of course this is now a manual process instead of an auto magic one so it’s a compromise)

Snapshots should not be persistent! They should only have a life of a few hours to a few days.  It is important to remove the snapshots since it creates a delta VMDK file and can grow quite large.  Also, if one creates many snapshots this can affect performance of the guest.

Personally I usually snapshot when the guest is powered down – this gives me the cleanest possible snapshot and I can revert to it with confidence.   It also means the snapshot is created instantly since the file system does not need to be quiesced.  Additionally, it is important to remember your VMware hypervisor can quiesce the file system (so long as VMware tools installed) but not necessarily the applications running in Windows.  i.e.:  SQL cannot be snapshotted reliably.

It is also very important to remember Snapshots are not backups in anyway shape or form. For “backup” purposes the entire VM package should be copied and compressed and stored on a medium other that the host running the VM.  i.e.:  I store my VM archives on my DIY NAS.

Disabling System Restore in XP: Right-Click My Computer and select properties and click the system restore tab, Select “Turn off System Restore” and click OK.
Disabling System Restore in Windows 7: Right-Click My Computer and select properties, click the System Protection link, Click the Configure Button and select “Turn off system Protection”, OK, OK

In conclusion, one can use snapshots in lieu of system restore to gain some performance in the Windows guest but it’s a compromise since the taking and deleting of snapshots is a manual process.

It is not a mystery to performance enthusiasts that hard drives are typically the slowest part of any computer.  I’ve always been curious about the Western Digital Raptor series of hard drives.  The original series was released in 2003 which makes this technology six years old.  Being “old” technology one can now purchase WD Raptor hard drives on eBay for a very reasonable sum, which I recently did.  These drives being “old” technology I was curious if they still hold up against the current crop of 7200 RPM hard drives.

I was using two test beds for this particular round of tests.  A 2006 Mac Mini running Snow Leopard and an Intel D945GCLF2 Atom 330 board running CentOS 5.4.

The hard drives tested were the aforementioned Western Ditigal Raptor, Western Ditigal Caviar Blue, Western Ditigal Green and an OEM Toshiba 2.5″ 5400 RPM drive.

The tests carried out were very simple, I used dd to write out a 4 GB file and then used dd to read it back.  Each test was carried out 3 times after a clean boot once the system had settled down.  The three passes were averaged to produce the final results.  Here are the dd commands I used:

time dd if=/dev/zero bs=1024k of=tstfile count=4096
time dd if=tstfile bs=1024k of=/dev/null

Throughput was calculated using base 2 (i.e.:  divide by 1024)

I also decided to add a couple of tests using mdadm raid 0 sets on the Linux test host.  raid was created with mdadm and formatted ext3 – I didn’t bother aligning the partitions.

Hard Drive Performance in MB/Sec

The results are really quite surprising.  First and foremost it is quite refreshing to see six year old technology still holding its own.  Though the WD Raptors are no longer setting speed records they are certainly fast enough to be usable.  We can also see that 7200 RPM hard drives have come a long way as far as performance goes.  Secondly we can see that the results varry quite a bit between the Mac Mini and the Intel D945GCLF2 motherboard.  Now it is impossible to compare the two directly due to OS and file system differences but we can certainly put come credibility in the results since both platforms are based on the Intel 945 chipset.

All in all the Raptors are impressive considering their age and will be used.

Sometimes you get an idea, Canadian Tire has a sale and tada you have a brand new Roomba to play with.  In this case a Roomba 530.  The Roomba has been very well documented and there are plenty of reviews out there so I’m not going to do that here.

With a 16 month old & a cat running around the house, there is little time to clean most days and it doesn’t take long till the main floor gets full of crumbs, Cheerios and  assorted pet bits.  It’s still early days but our Roomba has been able to clean up very well after our little monsters and with significantly less effort than pulling out the hose for the central Vacuum.  It’s even been profitable as it has some loose change in its dust bin this morning.

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