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I've noticed that on one of my VPSes ( debian 5 lenny ) ( not my linode ones but a host I used prior to linode ), the filesystem is very, very sluggish past midnight.

If I try to use the command line at all, it stalls. At some point after an hour or two, everything goes back to normal and it becomes usable.

Could it potentially be that the server was compromised? Has anyone run into something like this before?

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Could be they do some maintenance on teh underlying file storage? Like running antivirus (over the discs of the hosts)?

I ahve seen such behavior when a device uses a SAN and the SAN does stupid things like this, eating up all IO for "more important" things.

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You could look at your iowait statistics during this time as opposed to others. If your queue depth (avgqu-sz) or busy (%util) in iostat -x 1 is larger during this time only, then TomTom is right on the money. I don't remember how to look at this with sar. – zerolagtime Nov 30 '10 at 3:54
It is also possible that they are doing snapshots of your disks and have failed to prioritize the IO low enough to avoid impacting your QoS. But this is only likely if you have very limited bandwidth to your portion of disk. This is still "backups," but probably not in the way you expected it to mean. – zerolagtime Nov 30 '10 at 4:04

Meder - there are a few tools you could put into place to see what is happening.

You did not mention which OS you are using - so for now I will assume it is a linux based system...

  1. Install IOTOP and run from command line with the -o option.
  2. Install SYSTAT
  3. Run SAR and peek @ the results over a few hour period
  4. submit all to your host and ask them why - when TOP shows next to no traffic running - you are basically w/o a VPS to use
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+1 for analyzing first. nothing gives more weight to a complain than a full description of the trouble. besides, it will make it much easier and factual to check when they say 'fixed, try it again'. – Javier Nov 29 '10 at 9:41

As TomTom said, I would contact the host and see what sort of scheduled maintenance, if any, is performed during those hours. Most likely the VPS instance is being backed up or something. Sucky no matter the reason!

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