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Hard drive accessing every second with new Ubuntu install
Posted on 04-19-2014 20:19:45 UTC | Updated on 04-24-2014 01:39:31 UTC
Section: /software/ext4filesystem/ | Permanent Link

The annoying pulse

After installing the new Ubuntu (Xubuntu) 14.04, I rebooted the machine to the desktop. I noticed that the hard drive was being accessed every second consistently. Just pulse...pulse...pulse. It was driving me nuts, as I had no clue what could be causing it. Since this issue was IO related the easiest way to solve this was to install and run iotop.

Installing iotop and finding the perpetrator

# Install iotop
sudo apt-get install iotop

# Run IOTop with -o so we only see processes doing IO
iotop -o

# Output looked similar to this

Total DISK READ:       0.00 B/s | Total DISK WRITE:         2.00 M/s
TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>     COMMAND
 1    be/4 root     0.00 B/s    2.00 M/s   0.00 %     3.00 % [ext4lazyinit]

What the heck is ext4lazyinit?

Now I know anything in brackets is a kernel thread, and ext4 is the file system I used (Ubuntu uses) to format the partitions. Time to go see what this kernel thread does. After some digging I found the Git commit log for this ext4 file system feature.

Who wants a lazy file system?

In the old (or not so old) days of ext2 and 3 when you formatted the file system you would have to wait while it was created. Usually most of the waiting was because you had to wait for the inode tables to be created. Make a ext3 file system and watch how long it takes to make the inode tables. The bigger the drive the longer it takes to make these tables. We are talking 10 or more mins on 2TB drives and above. Ted Tso the creator of ext4 helped cut this time down by allocating some of the inode tables during creation and then allowed the rest of them to be made on first mount. When the file system is mounted the first time it sees this was marked to be done and creates a background kernel thread to finish creating the inode tables. This way your install time is cut down dramatically because you don't need to wait for the file system inode tables to be created. The are just happily created in the background as you work.

When will this bloody pulsing stop?

So how long will this take to finish? I'm not to sure as I left my machine on all night so it could finish. It was done by the morning so I can say less than 12hrs on a 1TB drive. Don't fret though it will eventually finish and rest assured there is nothing wrong with your hard drive or the install. This likely happens on older Ubuntu installs and any other distros that use ext4 as well.

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