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I get very high Write IO Wait time every time my back-up system from cPanel uploads the backups to a secondary storage server located underneath in the same rack.

They are connected directly on the secondary gigabite port using 30cm cable.

I tried both cPanel back-up systems and both are causing the same issue.

I have since disabled some fo the larger accounts, but that is not a solution.

Does anyone have an idea?

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    IOwait is not typically caused by network IO, but rather IO contention of your disk.
    – EEAA
    Dec 2, 2013 at 17:35

2 Answers 2

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Make sure you use incremental backups over FTP.

Consider using a 3rd party backup system like R1SOFT or another system. CPanel by default will dump and tar the backups locally and use your disk before sending the files over. But using the incremental FTP option will prevent taring of the files on the local disk.

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  • Agreed, except for the "use FTP" part. There is absolutely no reason to use FTP for anything now, and it is irresponsible to do so.
    – EEAA
    Dec 2, 2013 at 19:23
  • Curious. Why not use FTP and what should be used over FTP for learning purposes :)
    – Jason
    Dec 2, 2013 at 19:49
  • Well, for one, it's a cleartext protocol, so all file contents and credentials are sent across the wire unencrypted. Second, it requires two ports, and doesn't deal gracefully with NAT traversal in many cases. Instead of FTP, use scp/sftp, either of which are vastly superior to FTP. They use your existing ssh daemon, so there's no additional configuration overhead, and everything (credentials and data) is strongly encrypted.
    – EEAA
    Dec 2, 2013 at 19:55
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Under /proc/sys/vm you can set a lot which makes your writes faster. It is because the linux filesystem & vm developers like to make an irrational oft write cache flush, to make their work to see more stabile.

The next settings in sysctl.conf (and their commit with a sysctl -p) on the target system of your backup will be able to help a lot:

vm.dirty_background_ratio = 20
vm.dirty_expire_centisecs = 360000
vm.dirty_writeback_centisecs = 360000

Although it will make it sensitiver to power failures, IMHO it deserves its cost.

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