Multiple varnish instances per server?

Michael S. Fischer michael at
Sun Jun 1 19:38:24 CEST 2008

Why are you using Varnish to serve primarily images?  Modern webservers
serve static files very efficiently off the filesystem.
Best regards,


On Sun, Jun 1, 2008 at 8:58 AM, Barry Abrahamson <barry at>

> Hi,
> Is anyone running multiple varnish instances per server (one per disk
> or similar?)
> We are currently running a single varnish instance per server using
> the file backend.  Machines are Dual Opteron 2218, 4GB RAM, and 2
> 250GB SATA drives.  We have the cache file on a software RAID 0
> array.  Our cache size is set to 300GB, but once we get to 100GB or
> so, IO starts to get very spiky, causing loads to spike into the 100
> range.  Our expires are rather long (1-2 weeks).  My initial thoughts
> were that this was caused by cache file fragmentation, but we are
> seeing similar issues when using the malloc backend.  We were thinking
> that running 2 instances per server with smaller cache files (one per
> physical disk), may improve our IO problems.  Is there any performance
> benefit/detriment to running multiple varnish instances per server?
> Is there a performance hit for having a large cache?
> Request rates aren't that high (50-150/sec), but the cached files are
> all images, some of which can be rather big (3MB).
> Also, is anyone else seeing similar issues under similar workloads?
> --
> Barry Abrahamson | Systems Wrangler | Automattic
> Blog:
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