Logical vs. physical blocks on various media and how to detect
keiji_katata at post.pioneer.co.jp
keiji_katata at post.pioneer.co.jp
Tue Oct 11 20:24:07 PDT 2011
* From the T10 Reflector (t10 at t10.org), posted by:
* keiji_katata at post.pioneer.co.jp
Here are some additional information about optical discs. (I think you may
have so much interest in Optical disc especially. But it may increase your
1. DVD, BD have EDC on each 2K logical sector
So they have a lager ECC block size (32K, 64K) but may report uncorrectable
error on each sector by sector. Some important information such as file
may use only a 2K logical sector. So MMC devices should ignore error in other
remaining sectors in the ECC block.
2. Blocking (factor) field is placed in several commands response
Unfortunately MMC devices may not support 16 bytes length commands (READ
CAPACITY (16) command too). So to understand the mechanism, you may need to
check all places on MMC document those have word "Blocking".
On CD-R/RW, the Blocking factor is made other reason than ECC size (may be
similar with tape device). So there will be variations on a single CD-R/RW
For DVD/BD, you may check definition of "Recordable Unit".
Gerry Houlder <gerry.houlder at seagate.com>@t10.org on 2011/10/12 04:51:16
$BAw?.<T(B: owner-t10 at t10.org
$B08 at h(B: Peter Van Hove <peter at smart-projects.net>, T10 Reflector
<t10 at t10.org>
$B7oL>(B: Re: Logical vs. physical blocks on various media and how to
For direct access devices, there is a field in the READ CAPACITY (16) command
that returns the "number of logical blocks per physical block exponent". If
field indicates that there is more than one logical block per physical block,
then you will see the same behavior that you described for DVDs and CDs. Most
devices are still mapped 1 to 1 but next generation products are likely to
multiple logical blocks per physical block mapping.
Some existing SSD/ Thumb drive products actually put multiple LBs in the same
"physical block" but they still apply ECC correction on a "per logical block"
basis, so they still qualify as 1 to 1 mapping.
On Tue, Oct 11, 2011 at 1:06 PM, Kevin D Butt <kdbutt at us.ibm.com> wrote:
My response relates to tape devices. ?According to SSC-4r02 clause 126.96.36.199,
basic unit of data transferred by an application client is called a logical
block. Logical blocks are stored according to the specifications of the
for the volume and may be recorded as portions of one or more physical blocks
the medium. The mapping between physical and logical blocks is the
responsibility of the device server."
While not explicitly stating it, each tape vendor essentially determines what
the mapping is and it is vendor specific. ?But also, since tape supports
variable length blocks and it is its primary mode of operation, each physical
block contains x number of bytes (as determined by the vendor-specific
and each logical block is mapped into one or more physical blocks.
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
From: ? ? ? ?"Peter Van Hove" <peter at Smart-Projects.net>
To: ? ? ? ?"T10 Reflector" <t10 at t10.org>
Date: ? ? ? ?10/11/2011 10:40 AM
Subject: ? ? ? ?Logical vs. physical blocks on various media and how to
Sent by: ? ? ? ?owner-t10 at t10.org
I know that on CD, a logical block is also a physical block. ?The error
detection and correction is done on that one block and if block x is
blocks x-1 and x+1 may very well still be readable.
On DVD it is different. ?The logical block size is 2K but an actual
ECC block spans 16 of those logical blocks. ?Error detection and correction
applied to the 32K ECC block rather than every logical 2K block.
If one logical 2K block is unreadable, then infact 16 of those are unreadable
the entire ECC block is unreadable.
On Blu ray finally, the same principle but then 32 logical 2K blocks or a
physical block of 64 K.
I was wondering if I can apply the same logic on thumbdrives / SD cards, SSM,
Hard Drives etc.
I don't know however, if the same logic applies, how to get that information
|from a device, or is there a fixed number to be taken in account for every
media, such as for CD, DVD and BD ?
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at t10.org
More information about the T10