Re: Checksumming RAID?

[Roy Sigurd Karlsbakk <roy@karlsbakk.net>]

> > That doesn't make sense. Nearline and enterprise drives are large
> > 7k2 drives that come in consumer and enterprise models,
> 
> Nearline drives are in between consumer and enterprise.

Well, they are named enterprise…

> > Comparing "nearline" and "enterprise" like done here, is merely a
> > comparison of small and large drives, where it's well known that the
> > smaller (less dense) drives have less errors.
> 
> The paper I cited doesn't support this. The nearline SATA with
> hardware adapters to convert the interface to fibre channel. The
> enterprise drives were already fibre channel. The paper discusses the
> contribution of the adapter to checksum mismatches, but this alone
> doesn't account for all of the higher rate of error in nearline SATA.

7k2 "nearline" SAS drives exist from several vendors, with SAS interfaces without the need for adapters. Also, the interface, wheather SAS or SATA or FC, doesn't really mean much when the drive is the same. SAS (and FC?) has better timing and better controllers, but a SAS drive is a SAS drive nonetheless if it has a SAS interface.

> Further, the paper says "There is no clear indication that disk size
> affects the probability of developing checksum mis- matches."
> 
> At least when it comes to URE (which is not SDC), we note that the
> manufacturer specs are the same for a model regardless of disk size.

Then, if this is true, perhaps they should name their 4TB drives something else than "enterprise", which they do. Do you have more references on this part?

Vennlige hilsener / Best regards

roy
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Roy Sigurd Karlsbakk
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