Tape LBA vs. HDD LBA

Hello everyone,

I'm only just a neophyte on storage... and I desperately need your
help on these:

1. How are data stored in tape? I mean, the block addressing.
2. Is there any correspondence between Tape LBA and HDD LBA?

(I'm referring to Ultrium 1 and Ultrium 2 format... or do all tape
formats have the same block addressing methods?)

I've been searching for a sufficient resource material on Tape but
couldn't find one. I was kind of hoping you could recommend one.

I would really appreciate your help. Thanks a lot!

- Shiera -

On 28 Oct 2003 18:04:37 -0800, (Shiera) wrote:

1. How are data stored in tape? I mean, the block addressing.

Sequentially. Block n+1 follows block n. (I know that's pretty
useless, but it's about as good as you're going to get).

*How* useful (user) data is mapped to a given tape block is up to the
application doing the writing.

2. Is there any correspondence between Tape LBA and HDD LBA?

Nope. Except the obvious one, that they both address data. No
assumptions can be made about the data in a given block, or even that
the data in HDD blocks n and n+1 would be in tape blocks y and y+1.
Apart from anything else, HDD block sizes are almost invariably fixed
at 512 bytes, while tape blocksizes range from entirely variable up to
several megabytes.

(I'm referring to Ultrium 1 and Ultrium 2 format... or do all tape
formats have the same block addressing methods?)

No. However, generally speaking, a tape consists of between 0 and
some large number of (arbitrarily sized) blocks. Some tapes also
permit partitioning, which creates a number of arbitrarily sized
sections each of which behaves like a tape. A tape will generally
have both a logical end of tape and a physical one; the logical one
can be located at any position up to the physical end (in the case of
partitioned tapes, the physical end of tape is replaced with the
logical end of partition, which in the case of the last partition
usually coincides with the physical end of tape).

I've been searching for a sufficient resource material on Tape but
couldn't find one. I was kind of hoping you could recommend one.

Key concepts with tape:

Blocking is broadly just a way of defining IO sizes; the host will
request an IO of n blocks, where the size of each block was previously
agreed.

Host IO size is related to blocksize, but shouldn't be confused with
it. With variable sized blocks, the IO size defines the block, but
otherwise the IO is either a multiple of the blocksize or an exception
(e.g. end of tape) has occurred.

- Shiera -

Malc.

Try Elias AbuGhazaleh at novastore, they almost
invented tape backups!

Bob


On 28 Oct 2003 18:04:37 -0800, (Shiera) wrote:

|Hello everyone,
|
|I'm only just a neophyte on storage... and I desperately need your
|help on these:
|
|1. How are data stored in tape? I mean, the block addressing.
|2. Is there any correspondence between Tape LBA and HDD LBA?
|
|(I'm referring to Ultrium 1 and Ultrium 2 format... or do all tape
|formats have the same block addressing methods?)
|
|I've been searching for a sufficient resource material on Tape but
|couldn't find one. I was kind of hoping you could recommend one.
|
|I would really appreciate your help. Thanks a lot!
|
|- Shiera -

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