Subject: Re: DEV_B_SIZE
To: David Schultz <dschultz@uclink.Berkeley.EDU>
From: Steve Byan <>
List: tech-kern
Date: 01/31/2003 16:01:13
On Friday, January 31, 2003, at 02:24  PM, David Schultz wrote:

> If the disk corrupts a sector it was writing, that's already a
> problem for us.

 =46rom the Maxtor Atlas 10K III Product Spec:

Section 4.5.1 Power Sequencing

You may apply the power in any order or manner, or open either the=20
power or
power return line with no loss of data or damage to the disk drive.=20
data may be lost in the sector being written at the time of power loss.=20=

The drive
can withstand transient voltages of +10% to =96100% from nominal while
powering up or down.

> If the sector is 4K, that just makes it more of a
> problem.  With FFS and soft updates, we assume that the disk can
> atomically write 512 bytes, and we ensure filesystem consistency
> by establishing a safe partial ordering for metadata updates.  We
> expect that after a crash, either the old contents or the new
> contents of the sector are there.  I think we would need to
> implement journalling to ensure integrity if hard drives were
> likely to corrupt sectors on power failure.  (How often do they do
> this right now, and how often would they with 4K sectors?)

If you are doing nothing but continuously writing, the active data area=20=

covers more than 50% of the track, so you'd have more than a 0.5=20
probability of experiencing a corrupt sector. Derate this by your seek=20=

duty-cycle and your write disk utilization to arrive at the final=20

Steve Byan <>
Design Engineer
Maxtor Corp.
MS 1-3/E23
333 South Street
Shrewsbury, MA 01545
(508) 770-3414