Joomla Website Crashing Constantly After Moving to a Larger Hard Disk

A regular client called us a week ago and told us that, after moving his Joomla website to a larger hard drive, it started crashing constantly. We checked the load on his server and it was super high (in the double digits) which explained the constant crashing, but didn’t really reveal the root cause.

So, we checked the slow query log (since the process that was creating the majority of the load was MySQL) and we noticed that there was a huge number of various slow queries, which was odd, considering that the website was running very smoothly before the move to a larger hard drive. Naturally, we started optimizing the queries, one by one, but we just couldn’t get the website under control.

We then reduced Bing’s crawl rate, as well as Google’s (we did the latter task using Google’s Webmaster Tools). Things got better, and the website crashed less often, but it still crashed…

We then did another round of optimization, and we blocked all the spam and the non-essential bots, but the progress wasn’t substantial and the load was still un-maintainable.

We then remarked that around midnight, a cPanel process called pure-quotecheck was causing some additional load (second highest load after MySQL), and so we stopped it by disabling updates in WHM. The load decreased, but still, it wasn’t a silver bullet.

We literally worked for a week trying to optimize the website in order to get it back to stability, but we weren’t able to. We were ready to declare defeat, but, in a moment of despair, we re-read the first email that the client sent, which stated that the whole problem happened after the website was moved to a larger hard disk. So we thought, what if the new hard disk was not an SSD (Solid State Drive) hard disk (the previous hard disk was an SSD hard disk)? To our surprise, a quick test revealed that the new drive was a SATA (Serial AT Attachment) drive, which is around ten times slower than SSD! Aha! We found the root cause of the problem!

Immediately, we asked the hosting company to switch our client back to an SSD drive, which they managed to accomplish in a few hours, and, once they did, the website stabilized and became super fast (even faster than before the move because of all the optimizations that we did).

But how come we didn’t think of that before?

Our client communicated heavily with the host about this problem before resorting to us, so we couldn’t really imagine that it’s a hardware issue (although we did start suspecting that the hard disk was faulty near the end of our investigation, just before we discovered that it was a SATA drive). And honestly, we never thought that the host would do such a thing by mistake (moving a website from SSD to SATA).

But why would a switch from SSD to SATA have such terrible effects on a Joomla website?

Well, on large Joomla websites, MySQL tends to create a lot of temporary tables on the file system. As mentioned above, SATA drives are usually about 10 times slower than SSD drives when it comes to writing data, and so, on SATA drives, MySQL faces a bottleneck when writing those temporary tables. This leads to a huge load caused by MySQL waiting for the SATA drive to write the temporary tables. The problem, of course, is exacerbated as additional MySQL threads try to write some temporary tables, and have to wait in line until the previous threads are served by the SATA drive.

So, our dear reader, if your website starts crashing after moving to a larger hard disk, then make sure you were not moved, by mistake, from an SSD drive to a SATA drive. If that was the case, then ask your host to move you back to SSD. If that wasn’t the case, then please contact us. We always find a solution, our prices are affordable, and we are the friendliest developers on planet Earth.

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