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Slow backups with c1537a

Rob Pelletier
Occasional Advisor

Slow backups with c1537a

C1573A, using BackupExec V8.5 on a Novell 5.0 server...
The backup speed, on the SYS: volume only, is about 5.2 MB/min. On the MAIL: volume, I'm getting over 16 MB/min.
There are a few "unable to open file" file messages, but about the same number on each volume.
The backup, with verify, is taking over 12 hours, the total amount of data is only 4194 MB.
This is a new account for me, so I don't have much more info: DAT drive BIOS rev. BackupExec software rev., Novell SP level.
But it seems to me that, if I can get over 16MB/min on one volume, why not on the other?
I have attached the backup report...
10 REPLIES
Rob Pelletier
Occasional Advisor

Re: Slow backups with c1537a

Oops...

That's a C1537A (I've got fat fingers!)
Vincent Farrugia
Honored Contributor

Re: Slow backups with c1537a

Hello,

What type of tape cartidge are you using? DDS2 cartidges are slower than DDS3 ones.
Tape Drives RULE!!!
Vincent Farrugia
Honored Contributor

Re: Slow backups with c1537a

Hello,

I think yours is a DDS3 tape drive and you are using DDS2 from your performance rates, right?

Regarding the speed discrepancies, I think this is so because of the type of data itself you are backing up. If you enabled hardware compression (which is enabled by default), if the data is not very compressable, then the transfer rate will be lower than what you expect.

HTH,
Vince
Tape Drives RULE!!!
Rob Pelletier
Occasional Advisor

Re: Slow backups with c1537a

Thanks for your replies, Vince. Certainly a couple of bits of information that I was missing in there.
I have sent a message off to my client and will advise you, through the forum, of the outcome.

Thanks again.

RP
Michael Tully
Honored Contributor

Re: Slow backups with c1537a

Hi Rob,

From the product number you are definitely using a DDS3 tape drive. The correct tape media to use is a 125 metre tape or DDS3.
You wil experience a slightly slower input, but also not fit as much data onto a lesser
tape.

-Michael
Anyone for a Mutiny ?
Rob Pelletier
Occasional Advisor

Re: Slow backups with c1537a

I have confirmed with the client that she is definitely using DDS-3 tapes, so that theory goes out the window.

Any other ideas? I can't seem to see a problem with the drive or tapes, as the speed seems fine on the other volume...

Could this thing need to have the deleted files purged, or a vrepair, or some other Netware operation?

I've seen lots of backup problems (usually with lesser quality drives), but never had to deal with a throughput problem before.
Jan Klier
Respected Contributor

Re: Slow backups with c1537a

Rob,

Other factors that can affect your backup speed is the file system and general file characteristics as well.

If the same drive/cartridge is able to backup faster on one volume than another, I would look for a cause on the system, not the tape drive.

Factors that influence speed:

* compressability of data (already covered in other posts)
* fragmentation of disk (can cause heavy seeking which slows apps ability to pull data of disk, at some point possibly dropping below threshold datarate that allows streaming of tape drive, which results in dramatic decreases in backup speed).
* file size (typically many small files are harder to backup than very few large files, due to file system and backup software overhead; does your mail volume have only few large files??)
* other system activity activity during backup window (as your backups don't run at the same time, you may check if there is other user activity during one window, but not the other)
* sharing of the bus between the tape drive and other devices that have activity only at certain times.

Anyway, these are a few pointers to check out....
Rob Pelletier
Occasional Advisor

Re: Slow backups with c1537a

The tape drive is on its own SCSI card, and the backup occurs overnight, when nobody is using the server.

Looking at the backup log (attached earlier in the thread), you can see that the volume backup up more quickly has a bout 12,000 files for a GB of data, whereas the slower volume has about 50,000 files per GB of data. So you seem to be on the right track there.

It takes 10 times longer to backup that volume, but the throughput is listed as one-third...

This client does have a database that they use on a regular basis: it's not inconceivable that it could be fragmented on the drive. I can find nothing at the Novell web site on disk fragmentation, and therefore nothing on what to do about it.

I suppose I could restore the entire data directory from tape -- it would likely write the data in sequential bocks that way, although I can't be sure of that.

Funny, I've never seen anything like this before - there have to be a lot of servers out there with this much data on them, but I don't have any that backup this slowly...
Vincent Farrugia
Honored Contributor

Re: Slow backups with c1537a

Hi again,

Are you performing a full system backup on both cases?

You could try and backup using tar or fbackup some files on both machines (say like /home or /tmp). If the performance is the same, then the nature of the data (number of small files, fragmentation etc.) is the culprit. If not, then there must be another issue.

Just another check this one.

HTH,
Vince
Tape Drives RULE!!!
Jan Klier
Respected Contributor

Re: Slow backups with c1537a

Rob,

The one thing to understand when performance is involved is streaming of a tape drive.

Unfortunately this produces a rather dramatic effect. You would assume that the speed at which you feed data to how fast your backup is running is a linear function. For the most part it is, except for one big kink in the graph, and that is when the data feed drops below the rate at which the tape drive can continue to stream.

Tape drives write to the media while the media moves. And the media is typically moving at a constant speed (some higher end tape drives, such as LTO can use variable speed within a certain range to adjust). That means the system has to send the data tot he tape drive fast enough for the tape drive to continue writing at that speed. If the data come in slower, the drive has (what would be the CD-Rom equivalent of a buffer underrun) - except that instead of making a coaster (in CD-Rom cases) the tape stops the motor, backs up to where it left of, waits for sufficient data to come in and then resumes writing. However, this process of stopping, backing up, and resuming is very time consuming because of its mechanical nature. As a result the performance of a tape drive now suddenly drops dramatically.

Thus it is very important to be able to push data fast enough to a tape drive if you require the full performance.

And because of this inherent non-linear function, it is sometimes amazing what happens when you cross that threshold. So I wouldn't be surprised if your system is able to stream with the mail volume, but just falls short of the threshold with the 50,000 files, probably because of fragmentation or filesystem overhead.

There is a way to verify this on a Windows system (no, unfortunately these tools don't exist yet for NetWare, but the procedure can be used by booting the system in Windows or moving the tape drive to a Windows machine).

The diagnostics tool HP Library & Tape Tools can detect if your drive is not streaming from the drive logs. It calculates the ratio of start/stops vs. tape pulling hours. Connect the drive to a Windows system, download HP L&TT (http://www.hp.com/support/tapetools) and generate a support ticket. In the device analysis section it talks about these issues.