Thursday, 6 May 2010

DDN nightmare and muscle

We got a notable fright last weekend. Barça match against Inter in the Champions league semifinal was about to start when suddenly... crash. One of our flashy dCache pools serving a DDN fatty partition (125 TB, almost full of ATLAS data) got bananas.
The ghost of "data loss" was there, coming to us. Luckily, after a somewhat "hero mode" weekend for our MoD and experts (thanks Marc and Gerard!) following the indications of Sun-Support the problem could be solved with zero data loss (uf!). The recipe looks quite innocent from the distance: upgrade the OS to the last version, Solaris 10u8.
We find quite often that a solution comes with a new problem. This time was not an exception. The updated OS rapidly solved the unmountable ZFS partition problem, but it completely screwed up the network of the server.
We have not been able to solve this second problem yet, and this is why the 125TB of data of the upgraded server (dc012) were reconfigured to be served by its "twin" server (dc004). This is a nice configuration that the DDN SAN deployment enables. So this is I think the first time we try this feature in production, and there we have the picture: dc004 serving 250 TB of ATLAS data with a peak up to 600 MB/s... and no problem.
Looks like, besides OS version issues, the DDN hardware is delivering.

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