Improving Ext3 performance by placing the journal on a Flash Disk
Running a Linux Server on a HW RAID6 / LVM setup we are plagued by the fact that heavy activity on one file system will impact performance on all of them. If there is an active writer on one file system (especially meta data updates) then all other file systems will face extreme performance degradation. Especially read performance fell right through the floor. Response times become large and highly fluctuating.
The problem seems to even exist on simple single disk systems as is explained in this Ubuntu bug 131094.
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So tonight, after I had connected that new disk to a spare SATA port I was ready to go.
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Performance Impact
After running the setup for a few days, I draw the following conclusions:
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The general slowness of all file access, caused by a single heavy write is reduced so much that it does not interfear with daily work anymore.
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The hardlink backup (using rsync to keep a copy of the files, with hardlinks to those that have not changed) is about twice as fast.
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The tape based backup (bacula, running at the same time as the hardlink backup) is about twice as fast as well.
In other words, having an external journal with a HW RAID setup is a MUST.
I don't know if this is legit, but it looks neat.
