In article <[log in to unmask]>,
 Paul Wang <[log in to unmask]> wrote:
] Subject:      Re: sector atomicity
 
] Guy wrote:
] >Could someone elaborate on "sector atomicity" and why this feature
] >would confound the firmware in off-the-shelf SCSI discs?
]
] Sector atomicity means, as its name suggested, the whole sector is either
] completely written or nothing is written.  This is particularly useful
] when the power fails!
]
] Without this feature, a sector could be partially written if power fails
] in the middle of an I/O.  Subsequent read of this sector will result in a
] read error, since the ECC checksum won't match.  The end result is data
] corruption!  If this sector happens to be holding critical data, such as
] transaction manager log files, the whole volume set may be lost!
]
] Therefore I will never put my production data on non-HP disks.  For crash
] and burn test or development data, I think non-HP disks are OK as long as
] reload/data lost is not an issue.
 
I understand your concern.  Series II machines (early 70's) offered data
protection too.
 
I'm not a hardware ace, but it seems to me the issue is a matter of
maintaining power to the controller and drive long enough to be sure an
I/O operation is complete, internal (drive and controller) buffers are
written back and 'turn-off' orders are issued to the drive.
 
So what we're talking about is a mini-UPS?  Something I'm missing?
 
--
Regards  --  Tony B. Shepherd  --  [log in to unmask]
 
This opinion is worth what you paid for it, and if it proves to be wrong,
all monies paid will be cheerfully refunded upon presentation of receipt.