Monday, 5 November 2007

The Case of Decimal v. Binary

We all know that disk drive manufacturers have been conning us for years with their definition of what constitutes a gigabyte. There are two schools of thought; the binary GB, which is 1024x1024x1024 or 1,073,741,824 bytes and the decimal GB which is quoted as 1000x1000x1000 or 1 billion bytes. The difference is significant (7.4%) and something that has annoyed me for years, mainly for having to explain to "management" why the 100TB of storage they bought stores less than 100TB of data (significantly less with some manufacturers).

Seagate have just lost a class action law suit (see here) which means they are forced to give a 5% rebate to customers plus some free backup software.

Unfortunately, those of us who have purchased storage subsystems from vendors will not be able to claim as the case refers to customers who bought stand-alone units:

"You are a member of the settlement class if, between March 22, 2001 and September 26, 2007, you purchased in the United States a new Seagate brand hard disc drive from an authorized Seagate retailer or distributor, separately as a Seagate product that was not pre-installed into and bundled with a personal computer or other electronic device."

So I guess EMC/HDS/IBM can breathe easy at this stage. It does beg the question though, when are our large array vendors going to quote the real figures for the usable storage available on an array? I have various calculators I use to help me work out the usable storage (before and after LUN creation and with varying RAID types) as I need to present real rather than throretical figures when sizing arrays. I think we need some more transparency here.


BarryWhyte said...

I've always referred to this as 'marketing MB' vs 'engineering MB'

FYI, SVC uses the real thing, that is all the measurements shown are real 1024 based numbers. So specifiy 3GB and you get a 3GB virtual disk.

Stephen said...

The funny thing about this is that if you create a USP LDEV of say 100 GB, you need to multiply the MB by 1024. So 102400 MB = 100 GB. When I present that 100 GB to a host, it is 100 GB not 97.something GB.