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Title: Continuous disk access Author: Sandro Tosi Last modified: 2005-09-17 It might happened that you wonder `What the hell is accessing my disks: I'm doing nothing!'. Ok, first of all, explain what ``nothing' is; if you're burning a CD, you have to access the file to burn, and even if you're running a peer-to-peer program, disks accesses are normal. So make sure that really nothing ``strange'' is running on that machine; following the usual culprits: o Filesystem type Do you know what filesystem is on your disks? On recent installation there will be journaling filesystems. Such filesystems commit changes to disks at interval (for example, default EXT3 interval is 5 seconds), so if you noticed such regular access, maybe they are due to the filesystem and so you don have to worry about it. o ATime mount option For every file in the filesystem, the inode records three times: change, modify and access time; try $ stat <a_file> to see them. The atime (access time) it's written every time a file is accessed, even if the file is cached in RAM and so no disk access is needed. If an application keeps read a file (so it will be cached), the atime is written all the times, accessing disk. Since it's a mount option, to disable it you have to modify the /etc/fstab (or the mount command line) adding ``noatime'' into filesystem options. I've read this option increase the throughput of kernel.org of about 25%. o slocate/updatedb These programs do a full disk search for updating the ``locate'' database. When they are running you can see a huge stress on disks. You can even think to remove from cron daily run (default configuration) to put in weekly or manually execution. If the common causes before don't work, you could always # echo 1 > /proc/sys/vm/block_dump and monitoring the disk accesses with dmesg.