Re: [squid-users] cache disk failure handling?

Chris Woodfield wrote:
> Hi,
>
> Reading the squid FAQ, it's obvious to me that putting cache_dirs on a
> RAID (particularly RAID5) has serious performance penalties and is
> highly discouraged. However, what's not as clear is how squid deals with
> single-disk failures and whether or not it handles failures gracefully
> enough to obviate the need for RAID.
>
> If I have a squid running multiple cache_dirs on single disks, and one
> disk suffers a failure, how does squid respond? Will it simply stop
> using that cache_dir and soldier on, or can this cause an application
> crash?

Probably crash. Unfortunately Restart itself and crash again. Repeat...

>
> Also, when starting up squid, what is the effect of an unavailable
> cache_dir? I'm thinking of a situation where squid is restarted before a
> bad disk can be replaced.

If cache_dir is completely absent/missing squid will throw up a message
about needing -z option to create the cache and exit.

It should not be too much work to make the code ignore individual
cache_dir missing and accept if at least one is present.
If you are interested in sponsoring it let us know.

>
> If squid does have problems here, could using pairs of RAID1 partitions
> be an acceptable compromise, with the cost of reduced total storage?

It's the disk- write-duplication that slows the HDD and thus squid down
on all/most TCP_MISS objects. RAID without the duplication is much less
of a penalty, but still leaves you with the partially corrupt cache_dir
problem of possible crashes.

Amos

-- 
Please use Squid 2.6STABLE17+ or 3.0STABLE1+
There are serious security advisories out on all earlier releases.