>> On Fri, 20 Jan 2006 14:02:28 -0500, David Longo <[EMAIL PROTECTED]> said:
> I've just done a reconfig of my DB and LOG volumes that flies in the > face of conventional wisdom - but it works! [...] I think that most TSM admins tend to prefer as many ways to keep their pants up as can be arranged. I've mused in the past that, if IBM allowed 4 copies of a volume, than three would very quickly become de rigeur for standard running. (you -need- the unallocated copy if you're going to migrate to new disk tech) For a long time I used as many spindles as I could, to free database work of contention. With disk tech such as you are using now, and huge caches reliably inserted between you and the disk, the strength of that need has dropped precipitously. RAID on the back-end ameliorates many (but as has been pointed out, clearly not all) of the risks which the TSM-level mirror was intended to address. As a result, your 2:1 cost penalty for mirror disk allocation (mumble RAID overhead, mumble hot spare overhead) is being deployed to chase a smaller and smaller risk. It is entirely rational to conclude that, in your environment it is "too much" cost for "not enough" coverage. But I would very strongly suggest that you put numbers by that cost, and try to estimate the risk, too. Ever do dimensional analysis in physics or chemistry? Re-express 5 SATA disks in hours-of-service-down. :) I'm keeping the mirrors. - Allen S. Rout
