Just to steer things a bit off target...
Is there any advantage of either CDL or CMS formatting over the other? CMS
would require pre-processing before giving the disk to a Linux image, where
Linux can format the disk itself if it is doing CDL. Beyond that, are there
any speed or capacity issues? Block size advantages of one over the other?
Any other small gifts that could be presented by one and not the other?
--
.~. Robert P. Nix Mayo Foundation
/V\ RO-OE-5-55 200 First Street SW
/( )\ 507-284-0844 Rochester, MN 55905
^^-^^ -----
"In theory, theory and practice are the same, but
in practice, theory and practice are different."
On 9/21/07 12:06 PM, "Richard Troth" <[EMAIL PROTECTED]> wrote:
> Christian,
>
> Never assume that ECKD is CDL again, please. The CMS FORMAT command lays down
> a flawless array of 4k blocks before it stamps a CMS "EDF" filesystem on the
> volume.
>
> You are correct that FBA has no problem with unpartitioned media. But most
> other disk architectures do likewise, including SAN, copper SCSI, IDE, flash,
> CD ROM. In fact, unpartioned is the norm for CD ROM (or DVD) and is required
> for pseudo devices like loop back and logical volumes.
>
> CDL was a terrific addition, but its sole value is to simplify z/OS work. One
> could say perhaps it is CODDLING z/OS, perpetuating the myth that all the
> mainframe world is z/OS.
>
> CDL buys us nothing in a purely Linux environment, or even a mixed environment
> where z/OS does not reference the Linux volumes directly.
>
>
>
>
> -- R;
>
>
> ----- Original Message -----
> From: Christian Borntraeger [EMAIL PROTECTED]
> Sent: 09/21/2007 12:22 PM
> To: LINUX-390@VM.MARIST.EDU
> Subject: Re: Suse disk frustration
>
> Am Freitag, 21. September 2007 schrieb Richard Troth:
>> Skip the "partitioning" game. Put the filesystem on /dev/dasdd instead
> of /dev/dasdd1 and mount that. (be sure all this matches /etc/fstab, of
> course)
>
> Rick,
>
> Never suggest that again, please. You really have to know your systems very
> well before you can do that.
> It can work on FBA disks, but it will eat your file systems on ECKD disk,
> formatted with the compatible disk layout. The first track on ECKD disks
> usually has a different block size than the rest of the disk. As Linux only
> understands block devices with all blocks the same size, the dasd device
> drivers simulates a 4kb block on the smaller first blocks. As this block is
> only used for the partition table and not for data this is normally not a
> problem.The block is padded with e5.
>
> When you start to use the block as data block, you will lose data:
>
> // fill byte 1000-2999 of dasdd with zeros
> # dd if=/dev/zero of=/dev/dasdd bs=1 count=2000 seek=1000
> 2000+0 records in
> 2000+0 records out
> 2000 bytes (2.0 kB) copied, 0.00372012 seconds, 538 kB/s
>
> //it still looks fine
> # dd if=/dev/dasdd bs=1 count=2000 skip=1000 | hexdump
> 2000+0 records in
> 2000+0 records out
> 2000 bytes (2.0 kB) copied, 0.00397881 seconds, 503 kB/s
> 0000000 0000 0000 0000 0000 0000 0000 0000 0000
> *
> 00007d0
>
> //lets drop caches
> # chccwdev -d ec13 ; chccwdev -e ec13
> Setting device 0.0.ec13 offline
> Done
> Setting device 0.0.ec13 online
> Done
>
> //we now read e5 instead of zeroes. Data is lost!
> # dd if=/dev/dasdd bs=1 count=2000 skip=1000 | hexdump
> 0000000 e5e5 e5e5 e5e5 e5e5 e5e5 e5e5 e5e5 e5e5
> *
> 00007d0
> 2000+0 records in
> 2000+0 records out
> 2000 bytes (2.0 kB) copied, 0.0122469 seconds, 163 kB/s
>
>
> This behaviour is quite subtle, so please never suggest to create a file
> system or an lvm physical volume on a dasd without using a partition. It only
> works on a subset of available disk formats.
>
> Christian
>
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