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I have a number of spare external hard disk drives lying about the place and I was wondering if there is any practical way of using an external hard drive or USB flash memory drive to boost performance in Ubuntu?

The idea sprang from using a Windows PC and plugging in a USB device which prompted a pop-up asking whether I wanted the USB to be used for ReadyBoost to speed up my system. I imagine that this may well have no relevance to a Linux system but would be interested to know if there is any practical way of using an external hard drive for potential performance gain.

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up vote 7 down vote accepted

ReadyBoost improves things by caching boot files on media with fast access time. It's much like ureadahead but using an agile medium instead of just stacking the files on the boot disk. Whether or not it actually works better than something like ureadahead is highly debateable.

A Flash drive might have a lower seek time than a mechanical disk but throughputs are often very limited (there are exceptions of course: USB3 SSDs, for example). It's possible that by removing the seek element (as it does by stacking the files) ureadahead is faster because the drive has the faster throughput.

ReadyBoost has no effect on after-boot performance, IIRC, though it's concievable they might put some memory paging on there too if it's fast. You can put your swap on an external drive but that's only viable if the disk is faster, in both access and throughput.

In answer to your question: plugging a slow mechanical disk into a slow USB2 bus will give you no benefit other than extra disk space. Even if ureadahead could use it (which I don't think it can) any benefit would rely on the external drive having a higher throughput than your internal disk.

If that's the case (your internal disk is slow) you really want to consider upgrading it. Your primary disk should be the fastest permanent storage in your system. If you're considering an external swap, have a look at the prices of RAM. Stupidly high quantities are very cheap these days.

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Re: "ReadyBoost has no effect on after-boot performance, IIRC". That's actually incorrect. Consider: "Windows 7 use the Windows SuperFetch algorithm to determine which files should be stored in the cache. SuperFetch monitors files that users access (including system files, application files, and documents)". (source). Use Windows on a system with a slow hard drive, with and without ReadyBoost enabled, and it becomes evident that app startup times decrease when ReadyBoost is on. Not just for boot time. –  Chris W. Rea May 24 at 19:30
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I don't know of one, but I would think that any performance enhancement would be minimal. The effects of ReadyBoost is minimal anyways....

However you might want to look at this: http://ubuntuforums.org/showthread.php?t=395435

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