DLT speeds and multiple drives

[Roman Dijanosic]

Asking for some on-field information on practises backuping large amounts of data with DLT's.

Suppose you have DLT4000. From tech-specs I conclude
that max. speed of "backuping" is 9 Gb/hour. And from
speed of our backups I conclude that I am fully using
DLT4000 (regarding speed). If I am wrong please correct me.

So: backing-up cca. 45 Gb takes 5 hours. We have
tendention that this figure (5 hours) will rise in next
months considerably. So we will face that in time that
we have at night we won't be able to do backup's (which
naturely must be done).

My questions are:

- When (if) you face such problem did you "replace" DLT
with faster ones?
- Even the fastest possible DLT may on some system can
not be enough? Did you in such cases use DLT units with
several drives (same DLT with 2 drives gives you twice
the speed)? Is this "solution" well-known and
"world-wide" used? The data in question is of course
relational database. Of course then you have to modify
procedures so that separate file of database goes to
different drives (which is not problem). Only it gets
a little more complicted (regarding tapes) what forms
your "backup" (but O.K....)

Any "confirmation" that this is the "right way" would be welcome...

Roman D.

[Stefan Farrelly]

The limit for large backups like yours is how many SCSI controllers you have available for DLT drives. If you say have only 2, then you can only run 2x DLT drives and expect them to run at near full speed. If you put > 1 DLT on a single SCSI controller then they will run very slowly (they interfere with each other and slow each other down considerably).

So, if you only have (for example) 2 SCSI controllers and can therefore only have 2 DLT's which will run at full speed, if you still do not have enough capacity, or need the backups to run faster, then you only options are to replace the DLT's with newer faster ones (the DLT8000's are very fast), or purchase more SCSI controllers so you can add on another DLT and expect it to run at full speed.

[Printaporn_1]

Solution is using Omniback integration with database and it can perform parallel backup to several drives, no need to plan for placing of datafiles.

[Alexander M. Ermes]

Hi there.
A DLT 7000 has a performance of approx. 30 - 36 GB per hour, if you have only the DLT on the SCSI interface ( FWD SCSI ).

Sample :
Backing up 350 GB takes approx 3.5 hrs on 4 drives ( DLT 7000 )

RGds
Alexander M. Ermes

[A. Clay Stephenson]

The performance figures which have been quoted are correct and I can't stress enough the importance of 1 DLT per bus. It appears you are doing a cold backup (and I certainly trust them more than hot backups if you can spare the downtime).

There is a way you could do a cold backup and not care (within reason) how long it takes.

This is the scheme:

1) Shutdown the database.
2) Using the OnlineJFS vxfs snapof= option make a 'snapshot' mount of all your database filesystems
3) Restart your database - it's ready for normal use.

4) Backup the snapshots.

Steps 1 through 3 can be completed very quickly (< 2 minutes in my case).

You are then free to backup your snapshots and speed is no longer crucial. This has almost all the benefits of hot backups with the safety and convenience of cold backups. If you are using a utility like OmniBack you can script everything and it's all automated.

Food for thought, Clay

[Roman Dijanosic]

To: S.Farrelly, Printaporn, A.M.Ermes, A.C.Stephenson:

Thanks for answers so far, but I already more or less know all the informations that you told so far.

My message has rather different aim. The aim was did
you really decide for units with several drives? Did
your really replace "slow" DLT units with ones faster
ones with several drives? That in fact is my intention,
but involves "money" decision (so I need some kind
of confirmation that this in fact people do). You know:
You have something that works perfectly fine, you in fact just start to using it, but you "throw" it away (in a way)...

How several DLT must be put on machine (1 per SCSI),
tech-specs, OnlineJFS with snaphosts, Omniback possibilities,... this is already known to me.


Roman D.

[Stefan Farrelly · Accepted solution]

To answer your question. Yes. For HP's large email servers we replaced the old DLT4000's with 8x 7 DLT7000's per server (each on its own SCSI bus). This meant we could backup around 200GB in around 2.5 hours. For our servers here with single drives we have replaced the older DLT4000's for DLT8000's mainly because we need the extra capacity, not for speed, but the huge increase in speed is a bonus. If we had to backup any of our servers faster I would go for DLT8000's first (just one), and add one at time until we could get the backup time down to the desired level. The old DLT4000's we removed we didnt throw away, we sold them to an HP reseller who specialises in 2nd hand parts and got some money back to pay for the new ones.

I hope this is what you wanted.

[Ed Ulfers]

We chose to upgrade our DLT4000 library to DLT7000's for financial payback. The analysis included the increase in storage with the same tape supply, rather than buying more tapes to get the same value. The boost with backup speed was an addition that helped sell the deal to management.

Hope this helps,
-- Ed Ulfers

[Vito Sarducci]

Roman,

From my perspective of being a Veritas SRT Certified consultant, I can tell you that the evolution of DLT technology has moved fast.
Back less than two years ago, the DLT4000 was the standard HP was shipping, now its the DLT8000 with new systems. You answered your own question. Yes they have evolved to be replaced because HDW now is cheaper then SFW.

The DLT most installed from my experience in such large datacenters is the DLT7000. Very versatile, very stable drive that most Tape Library Vendors ship with their TLD's. The new SuperDLT is the way to go if your going to spend $$$ on getting latest and greatest HDW yet you can grow into this HDW.

ATL/Quantum is a good vendor from my perspective due to its technical support. I have seen them time and time again bend over backwards for customers. Im not trying to spoof HP, by far HP Technical Support is #1 in my book, but also look at ATL/Quantum.

Regards,

Chris
chrisam@rocketmail.com

[A. Clay Stephenson]

Hi Roman,

Yes I did replace the DLT4000's in one of our libraries with DLT7000's and did almost double performance. The limiting factor is often how fast you can feed these drives especially over
copper SCSI connections to disk arrays/disk drives.

The backup software also becomes crucial. For example, with OmniBack the speed of the database can limit performance if backing up a very large number of small files.

Obviously, there does come a limit to this even with Fibre and very fast tape drives. For this reason, you should also look at splitting mirrors, vxfs snapshots, TimeFinder, etc. to increase the size of your time window.

My 2 cents, Clay