Wednesday, April 19, 2006

Do Seagate drives sold by NetApp have some mystical powers? Not according to Hitachi!

I have been confused for years about the benefits of 512 (ZCS)Sector drives as compared to 520 (BCS) sector drives. And as one of our clients pointed out the R200 uses the older inferior 512 sector (ZCS), according to NetApp ZCS technology is inferior. So why would a newer unit, for example the R200, use superseded technology? I was confused and could not find an answer to this question from anyone at NetApp or from anywhere on their website. So I wrote a note to the guys at HDS. Since HDS works with NetApp on their Gfilers, I figured I could get a clear answer from them.


According to the HDS engineer
"There is no measurable difference in reliability between 512 byte and 520 byte sectors.
SCSI and FC drives can be low-level formatted with different sector sizes (within a small range with 512 at the low end).
The reason for this is that the payload of 512 bytes is sometimes augmented, as it is in Hitachi's case on the RAID and DF, by additional check byes appended to the end of the sector. I think Hitachi calls these CRC check bytes, but they also identify which sector it is, (perhaps by an "ID-less" technique where when the CRC bytes for the 512 byte sector are computed, a virtual ID field is included in the check bytes. That way, that sector will only read correctly when it is read from the right place.
So the bottom line is that this is a case of a subsystem vendor applied redundancy code applied on top of what the disk drive already supplies."

It leaves me with a feeling that all this drive jargon that NetApp has been marketing to us for several years is simply marketing spin. And another way to make their systems more proprietary.

Comments - from Jon Toigo on this post

Hey Mike, the really interesting thing to me is that NetApp contacted me through two different routes to describe how popular their solutions are for data protection. One fellow claimed that their gear was more popular than anyone else's for disaster recovery. When I invited them to make their case as a sponsor of the Disaster Recovery and Data Protection Summit, they demurred. Guess they were afraid that you would be there...

Jon Toigo
Toigo Partners International
Managing Principal
Data Management Institute

Founder
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Dunedin, FL 34698 USA
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jtoigo@toigopartners.com







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