big disk drives: a threshold

Lennart Sorensen lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org
Mon Sep 26 16:27:04 UTC 2011


On Sun, Sep 25, 2011 at 02:52:43PM -0400, D. Hugh Redelmeier wrote:
> I need to buy a new big disk drive.  Slow is OK.
> 
> 2T "green" drives seem to be a sweet spot.
> 
> WD 2T is $70 this weekend
> <http://www.canadacomputers.com/product_info.php?cPath=15_210_212&item_id=027811>
> 
> Other brands are a little more expensive or have shorter warranties
> (Seagate).

And a bad reputation for screwing up SATA drive firmware in very
serious ways.

> Samsung and Hitachi have the advantage over WD and Seagate that (I
> think) they let you set a bound on error recovery time, something you
> need to do if you are going to sensibly RAID the drives.  Soon Samsung
> and Hitachi will disappear from the disk drive market (their disk drive
> divisions have been bought by WD and Seagate -- scary).

WD used to have that, now they expect you to pay extra for a raid
edition drive.

> WD 3T green is $120 this weekend
> <http://www.canadacomputers.com/product_info.php?cPath=15_210_212&item_id=039030>
> Tempting, even though the price per byte is a bit higher.
> 
> I don't think I can use the 3T drive.  I hope I'm wrong.  So I'll lay
> out my reasoning:
> 
> - the WD30EZRX drive has 4K byte sectors.  I don't think that it
>   pretends to have 512 byte (earlier models did)

It apparently correctly shows as 4K physical sectors, 512 byte logical
sectors.  So that should be no problem.

You do have to use a recent enough kernel that it supports drives over
2TB correctly.  Apparently some older kernels at least on 32bit x86 are
limited to 2^32 logical sectors, and hence 2TB.  They will show the 3TB
drive as 800GB.

> - I don't think that older BIOSes (perhaps most without UEFI booting)
>   understand booting from 4K sectors.  Do new BIOSes get this right?

I believe all drives currently use 512 byte logical sectors, and the
bios just uses those.  As long as the bootloader is in the early part
of the disk I would not expect any problems with that.

> - as far as I know, none of my computers has a BIOS that knows about
>   UEFI.
> 
> Other issues:
> 
> - to use more than 2T, you need to use GPT partitioning OR larger than
>   512 byte sectors.

You really need to use GPT.

> - using GPT isn't a problem because it can be made to look enough like
>   an old fashioned partition table to get a BIOS to boot from it.
>   Once booted, Linux can handle GPT (and 4k sectors).
>   But it does take care.

Grub in the first sector of the disk using GPT works fine even if the
BIOS has no clue about GPT.

> - using larger than 512 byte sectors just to use the old fashioned
>   partition table probably isn't useful because so many old things
>   break with larger sectors anyway.

I would certainly expect things to break.

> Have I missed something?

Not sure.

-- 
Len Sorensen
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