Friday, April 14, 2006

Why does an R200 Nearstore use 512 Sector drives? What is going on? Maybe the reason that Dave Hitz is advocating Dual Parity now is because NetApp is using less reliable drives and drive technology?
A few years NetApp swtiched to 520 sector drives because they were more resilient . But on their Back up and Archiving units they currently use 512 Sector drives. Are the Maxtor ATA drives less error prone then the Seagate FC drives?

NetApp Disk Formatting: ZCS and BCS
Network Appliance filers in the early days came with with "normal" 512 sector disk drives. But the drive firmware's built-in check summing occasionally caused parity i
nconsistency, or data corruption.

So NetApp created their own method of check summing and introduced it in Data ONTAP 6.0. With this new method, every 64th strip on disk was a check sum of the previous 63. Unfortunately, performance suffered terribly, some say up to 30% overhead, until the engineers remembered the mainframe technology of old, where there were 520 sector disk drives with the check summing built right in to each sector. No more 64th strip and the performance was vastly improved.

As a result, the old, "normal" 512 drives became ZCS or Zone Check Sum--named after how the program slips the drive into zones of data stripes and check sum stripes. The new drives with the 520 byte sector became BCS or Block Check Sum drives because the check summing is "built-in".

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