Archive for November, 2009

Draytek Vigor 2820n Setup with Telefónica

Thursday, November 19th, 2009

In preparation for a probable change of ISP due to silly limitations on uplink speeds I recently bought myself a Draytek Vigor 2820n. I was quite surprised to see that this ADSL router which seems quite popular in the UK and the Netherlands is almost unheard of in Spain. I tried to get hold of one and found out why. There appear to be few distributors here and the price is rather unreasonably high. So I ordered one from BroadBandBuyer.co.uk and it arrived a few days later. For the price of  2 euros I got a UK to Spanish plug adapter and it was still cheaper than buying the router in Spain.

The inital setup to work with Telefónica didn’t take too long. The only thing that took some time was that as I use a fixed IP address I need to set various RFC1483 parameters and also my public static ip address, netmask and default gateway. These are the public values. This didn’t seem to work. I could see the ADSL connection come up but not see routing work externally.

In the end I found a link to this site (in Spanish) where it turns out that it’s necessary to explicitly force the link to be up as otherwise the filters on the Telefónica end make the Draytek think the line is down.

Once solved that got things working.

So next stop is to get the QoS working and perhaps I’ll get a better VoIP voice experience over the Internet. Let’s see.

Unlucky encounter with a Thecus N5200 Pro?

Sunday, November 15th, 2009

Remember Looking for an economic multi-disk NAS for home usage?

Two weeks ago I finally bought a Thecus N5200 PRO and put 5 x 1 TB disks in it in RAID-5.  This is a NAS box recommended to me by some colleagues.

After a week one of the disk started reporting soft SMART errors on disk 4 so I was intending to pull out the disk and change it. However a visit away from home for a few days this week delayed that.

While away, my wife showed a “friend” my new toy. He decided to open the “CD TRAY”, and pulled out disk 3…..

The Thecus got a bit upset about this as you can imagine and started beeping, but no data was lost. When I got in on Thursday night I added the disk back again and it began to rebuild the RAID-5 array, the process scheduled to take 15 hours.

After 6 hours the N5200 started beeping again, declaring the ARRAY damaged and …. away went all my data. Not very encouraging.  I checked the disks and they all reported ok with disk 4 still reporting the soft errors but no hard errors.

The Thecus logging (out of the box) is next to useless so I couldn’t see exactly what had happened or what had triggered the raid array to be broken. So about 100 GB of real data lost. Nothing really desparate, mainly some iTunes music, but a major PITA for a box I want to relay on for storage.

Since then I’ve locked all the drive doors to keep children, wives and friends from poking their fingers into my systems and have opened a ticket with Thecus to see if I did things incorrectly. However, I’m a bit concerned by what happened as the whole point of this box is to safely store data for me.

Moral of the story:

  1. lock all disk drives EVEN at home.
  2. Add stickers on the box saying DO NOT TOUCH
  3. Test/burn in the drives first to make sure they are in good order before you start
  4. Test recovery procedures before using the system in real life.
  5. RAID-5 repair seems more dangerous than you might expect.

Doing all of this type of preparation takes a while and means you can not use the new storage device for quite a while. Perhaps that’s better than losing data.  None of this will sound new to anyone in a professional environment but even at home it seems to be necessary.

And I never understand how normal people who just use a USB external disk never seem to have disk failures or problems…

So was I just unlucky?

Thoughts on MySQL 5.1 and later

Thursday, November 12th, 2009

It’s been a while since I’ve posted anything new. In the meantime I’ve been pretty busy. Working on production systems often means that you are not running bleading edge. That’s fine but sometimes you need to look at doing the upgrade and to do that you have to do quite a few checks to see how well newer versions of the software you use will work.

I’ve been in that situation with MySQL. I have quite a few boxes most of which are 5.0 and have been working fine. MySQL-5.1 has been GA now for some time, and I have started to look at it as support for 5.0 is about to end.  I’ve already found quite a few 5.1 bugs, good enough to crash the server, but again that’s to be expected. Heavy loads and odd usage of the server means that MySQL can never be able to test all things.  Replication problems caused a few issues with the first versions of 5.1 but they all seem to have been ironed out now.  The other main headache I experienced was upgrading one specific mysql 5.0 instance. It proved quite painful. Turns out that this is mainly due to problems if you have stored procedures or triggers and the rather awkward process you need to go to upgrade in these circumstances.  Something to go into more detail at another time, but improving the upgrade procedure is something that MySQL should really look into. My conclusion is that people just don’t use triggers or stored procedures, except at least for very simple stuff. Perhaps those that do like to suffer in silence?

Those of you who do not have triggers or stored procedures of course will wonder what all the fuss is about. Other boxes I’ve upgraded just work without almost any effort at all.  Really, really easy.  So just be aware that your mileage may vary.

One thing is getting the upgrade done and seeing that things seem to work fine. For me many of the boxes are replication slaves so it is necessary to check that replication works too. The final task is to check the box under load. That is the real test of any new version of software. See how it goes under real load and compare the numbers. If you are lucky you get extra features AND better performance. If you can: load the box until it breaks. Do that also with the old version on the same hardware and then you can see how they compare. In spite of all these synthetic benchmarks you can run, realistic testing is so much more convincing.

So that is what I’ve been doing by making a simulated load from web users and applying it to a MySQL server. I was not sure what to expect and some contacts had reported worst performance on 5.1 compared to 5.0. I have been pleasantly surprised. MySQL 5.1 does perform a lot better than 5.0, and while I am not looking to use it, 5.4 is so much better still.  That is, the same hardware can take about 20-30% more load on 5.1 vs 5.0 and about the same again on 5.4 vs 5.1. I would like to use 5.4 but it is not going to be GA so I will have to wait for 5.5 or whichever version MySQL decides to push out after 5.1. Nevertheless, it is nice to know that things are better and there is more improvement to come in the future. It may be worth pointing out that these tests were done on new 16-core machines with quite a lot of memory (48 GB). It’s been known that 5.0 does not scale well past 4-way servers, and 5.1 has some limitations as the number of cores increases. Sun has been trying to fix this with 5.4 and it shows. Good stuff.

Moving to 5.1 looks promising and is worthwhile. If MySQL can get some of the 5.4 performance improvements out soonish then that will be even better. Do your experiences with the newer versions of MySQL co-incide with mine?