A computer components & hardware forum. HardwareBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » HardwareBanter forum » General Hardware & Peripherals » Storage & Hardrives
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

What's so great about tape?



 
 
Thread Tools Display Modes
  #21  
Old September 4th 03, 09:54 PM
David Magda
external usenet poster
 
Posts: n/a
Default

(Peter da Silva) writes:

Amanda does too.


Really? Last time I looked it didn't. I'll have to update my knowledge.

In the situation we're discussing, being able to do just one tape a
night is an *advantage*.

[...]

ACK. Misunderstood what was being said.

--
David Magda dmagda at ee.ryerson.ca,
http://www.magda.ca/
Because the innovator has for enemies all those who have done well under
the old conditions, and lukewarm defenders in those who may do well
under the new. -- Niccolo Machiavelli, _The Prince_, Chapter VI
  #22  
Old September 5th 03, 06:55 AM
Rob Turk
external usenet poster
 
Posts: n/a
Default

"Dan Foster" wrote in message
...
In article , Boll Weevil

wrote:

See if you can add this up. To start, we have about 200 Sun servers and
about 1200 NT servers. About 100 Sun servers and about 100 NT servers
are on the SAN and share the following EMC and Hitachi subsystems:

7 EMC 8830 frames with about 13 TB raid 10 useable, each
1 Hitachi 9980V frame with about 45 TB raid 5 useable

There are a whole lot of direct attached SCSI disk arrays and internal
disks in each of the 1200 NT servers. I can't even start as to how much
storage these servers account for. These all get backed up.


Rough calculations shows that using hardware compression for a LTO-2

setup,
one could do all of the above in about 2 (or so) fully decked out IBM 3584
LTO libraries (just as an example), assuming an average size of directly
attached storage for each of the NT servers being 1 TB. A decked-out LTO-2
library with 6 frames should yield in the neighborhood of about 720 TB of
tape storage capabilities.

If 1200 servers * 1 TB = 1200 TB; that'd be one decked out LTO library and
a second library with about 240 TB of available tape space. For the other
stuff... 13 * 7 = 91 plus 45 TB = 136 TB. So you'd still have 104 TB of
free data space, and capable of doing a single full backup for everything
with two libraries and about 3500 tapes.

This assumes 400 GB (hw compressed) LTO-2 tapes; if you are using 20 GB
tapes in uncompressed mode, then your tape requirements goes up by 20

times
3500 for at least 70,000 tapes. Also, if the average per-NT server for
storage is other than 1 TB, that would also influence number of tapes
required, as well.

-Dan


Capacity-wise you're probably correct, I didn't do the math. However, many
of these types of setups have a different limiting factor, being the number
of changes per hour that a tape robot can handle or the number of drives
available. You'd need enough drives to keep the robot busy and a fast enough
robot to keep the drives going. This all depends on the access pattern. If
such a system is used for record based archives then you'll usually need a
lot more exchanges per hour than in a pure backup environment. The fastest
Powderhorns do about 450 exchanges per hour. Just inserting a separate
cartridge for each of the 1400 systems takes 3 hours, assuming one robot and
unlimited drives. Cascading robots help bring this to a lower number.

Also, with this many systems, even if you are doing backup only, you will
run into the issue if the number of parallel tasks you can run. You need a
large number of drives in order to give each system a chance to access one,
or you need to revert to backup software that can combine (multiplex)
several data streams into one.

To make a long story short, capacity is only one factor of many when dealing
with a setup as large as this.

Rob


  #23  
Old September 5th 03, 09:16 AM
Rob Turk
external usenet poster
 
Posts: n/a
Default

"Paul Rubin" wrote in message
...
"Rob Turk" writes:
For Exabyte drives, for 8200's no mods were needed. The firmware (32KB

of
code on an 8051 CPU) did not require any changes to space to the next
filemark after EOD. Not enought smarts to detect EOD while spacing ;-)

For
all other 85xx drives a standard EE-image implementing 'directory

support'
allowed you to do the same thing. No tricks, no switching power, just

using
the features of the drive.


Thanks, that helps. How is the situation for current Exabyte/Ecrix

drives?

Also, suppose you have an M3 or VXA2 cartridge and cut the tape
somewhere in the middle with a scissors. Can you get back (most of)
the data from both pieces without having to go too crazy with special
programming? Is there enough redundancy to not lose data around where
the cut is? I figure you can't splice the tape, but maybe you can
spool each piece onto another cartridge or something.


If you cause physical damage to the media, you will need to resort to rigged
decks and specialised recovery techniques to get the data back. Just like
you would have to if you open up your harddisk and scratch the platters.
That level of recovery isn't part of standard functionality in any consumer
product. With the VXA-2 packetised data format, the chances of getting
everything back is pretty good, if the cut is clean. Physically the blocks
that are cut through are beyond repair, but the logical format allows for a
lot of missing blocks through multiple levels of ECC correction. Due to the
way data is written, tape deformation is also not an issue.

With most other tape technologies (including M2) you will likely lose the
data blocks/tracks that are physically damaged, but everything before or
after should be recoverable. Just not on a consumer deck ;-)

Rob


  #24  
Old September 10th 03, 01:23 AM
Eric Lee Green
external usenet poster
 
Posts: n/a
Default

In article , Anton Rang ruminated:
Eric Lee Green writes:
In article , Malcolm Weir ruminated:
Tape's failure modes tend to be less catastrophic than disk's. E.g.


That is not my experience. In general, when a section of tape becomes
unreadable, every bit of tape after that section is no longer
accessible.


I've never seen a drive which behaved that way. Are you sure it's not
the driver on your system refusing to skip past the bad block?


Could very well be. I haven't had bad tapes in a long time. The last time
was back when I was doing SCO Unix, which was seriously broken in a number
of other ways too.

--
Eric Lee Green
Linux/Unix Software Engineer seeks employment
see http://badtux.org for resume


-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Cannot eject tape from PV 120T DLT1 Autoloader drive [email protected] Dell Computers 3 January 25th 05 09:56 PM
Great storage method, is it available in UK??? Mark General 5 March 14th 04 11:58 AM
ati video on demand is great - export sucks Nicholas Tse Ati Videocards 1 August 28th 03 05:11 PM
cutting psu wires Pen General 4 July 27th 03 07:49 PM
Records great, but what about the audio??? mxh Ati Videocards 7 July 22nd 03 05:37 AM


All times are GMT +1. The time now is 06:26 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 HardwareBanter.
The comments are property of their posters.