IBM DS8700, Introduction And Planning Manual

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Count key data
In count-key-data (CKD) disk data architecture, the data field stores the user data.
Because data records can be variable in length, in CKD they all have an associated
count field that indicates the user data record size. The key field enables a
hardware search on a key. The commands used in the CKD architecture for
managing the data and the storage devices are called channel command words.
Fixed block
In fixed block (FB) architecture, the data (the logical volumes) are mapped over
fixed-size blocks or sectors.
With an FB architecture, the location of any block can be calculated to retrieve that
block. This architecture uses tracks and cylinders. A physical disk contains multiple
blocks per track, and a cylinder is the group of tracks that exists under the disk
heads at one point in time without performing a seek operation.
T10 DIF support
American National Standards Institute (ANSI) T10 Data Integrity Field (DIF)
standard is supported on System z for SCSI end-to-end data protection on fixed
block (FB) LUN volumes. This support applies to the IBM Storage DS8800 unit
(models 951 and 95E). System z support applies to FCP channels only.
System z provides added end-to-end data protection between the operating system
and the DS8800 unit. This support adds protection information consisting of CRC
(Cyclic Redundancy Checking), LBA (Logical Block Address), and host application
tags to each sector of FB data on a logical volume.
Data protection using the T10 Data Integrity Field (DIF) on FB volumes includes
the following features:
v
Ability to convert logical volume formats between standard and protected
formats supported through PPRC between standard and protected volumes
v Backward compatibility of T10-protected volumes on the DS8800 with non T10
DIF-capable hosts
v Allows end-to-end checking at the application level of data stored on FB disks
v
Additional metadata stored by the storage facility image (SFI) allows host
adapter-level end-to-end checking data to be stored on FB disks independently
of whether the host uses the DIF format.
Notes:
v This feature requires changes in the I/O stack to take advantage of all
the capabilities the protection offers.
v
T10 DIF volumes can be used by any type of Open host with the
exception of iSeries, but active protection is supported only for Linux on
System z. The protection can only be active if the host server is Linux on
System z-enabled.
v
T10 DIF volumes can accept SCSI I/O of either T10 DIF or standard
type, but if the FB volume type is standard, then only standard SCSI I/O
is accepted.
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Introduction and Planning Guide
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