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Home > Archive > Data Storage > October 2005 > Question on Tape file system (NTBackup)
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Question on Tape file system (NTBackup)
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| arizvi 2005-10-12, 6:01 pm |
| Hi,
Is there some information on what the file system created by NTBackup
looks like. I am new to storage technologies but I am familiar with FAT
and NTFS file systems. If you can point me to the right source or
explain the overall architecture, I'd be grateful.
Thanks,
Ahmad
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| Rob Turk 2005-10-12, 6:01 pm |
| "arizvi" <ahmadwaris@hotmail.com> wrote in message
news:1129066075.952847.318600@g47g2000cwa.googlegroups.com...
> Hi,
>
> Is there some information on what the file system created by NTBackup
> looks like. I am new to storage technologies but I am familiar with FAT
> and NTFS file systems. If you can point me to the right source or
> explain the overall architecture, I'd be grateful.
>
> Thanks,
> Ahmad
>
Go to Microsoft's knowledge base and search for 'Microsoft Tape Format', or
MTF. There's supposed to be a full spec on their site somewhere. Here's a
first start: http://support.microsoft.com/defaul...kb;en-us;104223
Rob
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| arizvi 2005-10-13, 5:55 pm |
| Hi Rob,
I have one more question: is file data contiguous in a data stream, or
are parts of files stored in different location on tape, as in hard
drives. It seems to me as if files are stored completely contiguous on
tapes.
Thanks,
Ahmad
Rob Turk wrote:
> "arizvi" <ahmadwaris@hotmail.com> wrote in message
> news:1129066075.952847.318600@g47g2000cwa.googlegroups.com...
>
> Go to Microsoft's knowledge base and search for 'Microsoft Tape Format', or
> MTF. There's supposed to be a full spec on their site somewhere. Here's a
> first start: http://support.microsoft.com/defaul...kb;en-us;104223
>
> Rob
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| Rob Turk 2005-10-13, 5:55 pm |
| "arizvi" <ahmadwaris@hotmail.com> wrote in message
news:1129216743.530701.284990@g49g2000cwa.googlegroups.com...
> Hi Rob,
>
> I have one more question: is file data contiguous in a data stream, or
> are parts of files stored in different location on tape, as in hard
> drives. It seems to me as if files are stored completely contiguous on
> tapes.
>
> Thanks,
> Ahmad
Yes, files are stored contiguous on tape. This used to be a trick to defrag
harddisks, simply restore the entire disk from tape..
Modern backup packages can use a technique called multiplexing. This
interleaves multiple backup streams to improve backup performance and keep
tape drives streaming. The side-effect is that files are intermixed as well,
so no longer contiguous. Standard NT backup doesn't use multiplexing, so no
worry if that's your target format.
Rob
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| arizvi 2005-10-13, 5:55 pm |
| Another question, and I hope its my last one. What is a filemark? Is it
a sequence of bits and bytes that indicates condition like EOF? I guess
my question is: Is it on the hardware or software level?
>
> Yes, files are stored contiguous on tape. This used to be a trick to defrag
> harddisks, simply restore the entire disk from tape..
>
> Modern backup packages can use a technique called multiplexing. This
> interleaves multiple backup streams to improve backup performance and keep
> tape drives streaming. The side-effect is that files are intermixed as well,
> so no longer contiguous. Standard NT backup doesn't use multiplexing, so no
> worry if that's your target format.
>
> Rob
| |
| Rob Turk 2005-10-13, 5:55 pm |
| "arizvi" <ahmadwaris@hotmail.com> wrote in message
news:1129226946.430260.81100@g44g2000cwa.googlegroups.com...
> Another question, and I hope its my last one. What is a filemark? Is it
> a sequence of bits and bytes that indicates condition like EOF? I guess
> my question is: Is it on the hardware or software level?
>
A filemark is a bit sequence or signal on tape that the tape drive
recognises as a marker. Since tape is sequential, it's hard to position to a
specific location. On disk you have a directory that points to a specific
cylinder-head-sector combination, on tape there's no such thing.
The backup software could write filemarks during a backup to allow quick
restores later on. The software would for instance write a filemark every
100 files or so. On a restore of file 750, the software can tell the
tapedrive to fast-forward to filemark #7, and then start reading through the
data until it hits file 750. Without filemarks it would have to read all
data on tape until it reaches the desired file.
NT Backup doesn't use filemarks that way, it uses them to mark the end of a
dataset and the end of index information. This makes it easy to quickly
retrieve the file index (tape directory) and then perform the actual
restore.
Rob
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| arizvi 2005-10-24, 9:43 am |
| Hi Rob,
I have been analyzing a tape dump, in which the tape was made by
NTBackup.
A portion of the tape structure is as follows:
FILE DBLK followed by STAN(dard) Data stream (file data)
The file DBLK and stream header both contain the size of the data (file
size). However, when I calculate the end of data by adding: File Begin
+ File Size, I get an offset in the tape dump which does not seem to
equal the next File DBLK. For example:
File Begin Offset = 4096
File Size = 0x00137CF8 = 1277176 (from FILE DBLK)
File End should be = 1277176 + 4096 = 1281272
But the next FILE DBLK or stream header does not start from this
offset.
I dont know what I am doing wrong. Any ideas?
Thanks,
Ahmad
>
> A filemark is a bit sequence or signal on tape that the tape drive
> recognises as a marker. Since tape is sequential, it's hard to position to a
> specific location. On disk you have a directory that points to a specific
> cylinder-head-sector combination, on tape there's no such thing.
>
> The backup software could write filemarks during a backup to allow quick
> restores later on. The software would for instance write a filemark every
> 100 files or so. On a restore of file 750, the software can tell the
> tapedrive to fast-forward to filemark #7, and then start reading through the
> data until it hits file 750. Without filemarks it would have to read all
> data on tape until it reaches the desired file.
>
> NT Backup doesn't use filemarks that way, it uses them to mark the end of a
> dataset and the end of index information. This makes it easy to quickly
> retrieve the file index (tape directory) and then perform the actual
> restore.
>
> Rob
| |
| Rob Turk 2005-10-24, 9:43 am |
| "arizvi" <ahmadwaris@hotmail.com> wrote in message
news:1129582460.348045.315570@g49g2000cwa.googlegroups.com...
> Hi Rob,
>
> I have been analyzing a tape dump, in which the tape was made by
> NTBackup.
> A portion of the tape structure is as follows:
>
> FILE DBLK followed by STAN(dard) Data stream (file data)
> The file DBLK and stream header both contain the size of the data (file
> size). However, when I calculate the end of data by adding: File Begin
> + File Size, I get an offset in the tape dump which does not seem to
> equal the next File DBLK. For example:
> File Begin Offset = 4096
> File Size = 0x00137CF8 = 1277176 (from FILE DBLK)
> File End should be = 1277176 + 4096 = 1281272
>
> But the next FILE DBLK or stream header does not start from this
> offset.
>
> I dont know what I am doing wrong. Any ideas?
>
> Thanks,
> Ahmad
>
Hi Ahmad,
I can't answer your question without having to dig into the NT tape format
again myself. It's been years since I've looked at the NT tape format at
that level of detail. That's a bit beyond 'free advice on a newsgroup',
that's pretty close to data recovery consultancy. Wanna hire me? ;-) I'm
afraid you're on your own trying to figure this out.
I'd start by making simple NT backups of just single files or two files and
then see what shows up on tape. Maybe there's data padding going on, maybe
the format description has been changed from the time the MTF 1.0 document
was written. Who knows...
Good luck,
Rob
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| arizvi 2005-10-24, 9:43 am |
| Thanks Rob,
You have been more than helpful.
Regards,
Ahmad
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