[Beowulf] Problem with Single RAID disk larger than 2TB and Linux

Guy Coates gmpc at sanger.ac.uk
Wed Oct 3 09:27:35 PDT 2007

Jon Forrest wrote:
> Guy Coates wrote:
>> Luns over 2TB are a bad idea. There are just too many reasons why they
>> might not
>> work, and trying to track down the right one is a pain.
> Other than the usual putting all your eggs into one basket problem,
> why should a lun over 2TB containing an ext3 file system, be any
> more risky than those under 2TB, assuming all the partition table
> issues are resolved? Are there performance, reliability,
> compatibility, or other problems?

You are right; luns over 2TB are not any more risky than luns under 2TB. If they
work "out of the box" on your particular setup, great.

However, if they don't work then you are into a world of pain working out
whether it is your storage controller, SAN fabric, HBA, multipath
implementation, kernel, partition table or filesystem which is broken.

It gets especially bad in SAN environments where you have multiple
kernel/storage combinations. Keeping luns < 2TB means that there is a reasonable
expectation that things will keep on working when you change the storage



Dr. Guy Coates,  Informatics System Group
The Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1HH, UK
Tel: +44 (0)1223 834244 x 6925
Fax: +44 (0)1223 496802

 The Wellcome Trust Sanger Institute is operated by Genome Research 
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