Compaq DAT 20/40

[Dave Dewar]

Hi Scott,

Let me know how you got on. As I said previously I know know much about your system so its difficult to make additional suggestions over and above whats in the performance troubleshooting guide which is pretty exhaustive.
If you are still having problems, give me a quick run down of your system and we will take it from there.
One point though, did you run the tool called PAT to check you disk performance? If your disk subsystem is not fast enough and/or heavily fragmented, then basically the data doesn't get supplied to the drive fast enough and the effective transfer rate with go down.

Cheers,

Dave Dewar

[Scott_186]

Dave.. I ran every tool that was on that page.. Yes, I ran PAT too.. the read/write was 6mb/s so that's ok..

Here's what I got:

4 Windows 2000 servers, all updated from nt4 in January (the last time the drive worked good) and they all have every update ever released.. sp's, drivers, etc.. 1 NT4 server, just doing faxxes.. I installed the Arcserve client agent on each machine last night..today when I got in the backup job was asking for another tape cause it ran out of room! ROOM? It only backed up 2 servers that between the two have maybe have 16 gig.. It's gotta be the compression, but I think it checked out ok with those tools..

[Dave Dewar · Accepted solution]

Hi Scott,

Hmmm, I am still not sure of you system setup here, bear with me if I am being a bit thick :-). My guess from what you are saying is that you have 4 W2k servers, networked and one of these has a Compaq 20/40 DAT drive connected to it. You also have an NT server as well on the same network, making a total of 5 servers.

You are backing up all five servers to the single DAT drive on one of the servers.

You are using Arcserve backup software.

Is this correct so far?

You have patched everything to the latest level.

The performance tools indicate your drive can operate as designed at speeds in excess of 6MB/s when you run them on the server with the tape drive connected.

What is the speed of your network? 100baseT? What configuraton are you running? Are all the servers connected to a single hub/switch?

What happens if you just perform a backup of the tape drive server? Do you get good performance? I wonder whether it is a network issue, or something to do with Arcserve client agents.

I still don't know what SCSI HBA you are using, but am assuming you have patched the drivers up to the latest.

As to why you are apparently getting less than native cpaicty on your tape and few possible answers are:
It is possible that if you have a poorly performing drive to actually waste capacity on the tape as the drive has to do lots of rewrites and so end up with less than native capacity. You have checked this on LTT and everything seems fine.
You could also have software and hardware compression turned on a the same time. This can result in data expansion and again lead to acheiving less than native capacity as observed by the user. You should be able to check this in the Arcserve backup options. Again, I am assuming you have already checked this.
Finally, if the type of data you are backing up is predominantly compressed data, zip, jpeg etc, then data expansion can occur with either software or hardware compression.
Tina's links explain all of this, but you have said you are familar with this, so we can discount it.

Anyway,

Have a good weekend, we can continue this on Monday if you are still having issues.

Cheers,

Dave Dewar.

[Scott_186]

Hi Dave

Yep, what you said about the 5 servers and one DAT drive is correct. We are runing a windows 2000 network (tcp/ip) and all servers are connected to a 100mb switch, oh, the servers are all 100mb too.. You name it though, I got the latest drivers for it.. EVERYTHING inside those servers is up to date, patches and all.. What exactly is a SCSI HMB though??

The server that the DAT sits in, backs up just fine in under an hour..so that is working fine.. Maybe it is the network, but I can't figure it out if it is.. I'm running the backup tonight on the primary server and one win2k server with the agent installed.. I'll let ya know how that goes..

I really appreciate your help Dave..

[Dave Dewar]

Hi Scott,

SCSI host bus adapter (HBA) (scsi controller card conencted to tape drive). Since, you get good performance standalone I think we can discount this.

With a 100baseT link max possible transfer rate is 10MB/s so one would think that would be ok.

I am not very familar with Arcserve client agent backup. I'll find some time to talk to one of our solutions engineers about this today to see if they can provide any pointers.

Cheers,

Dave Dewar.

[Scott_186]

This is my summary from last nights job:
*********************************
Backup Session Cancelled
155,429 directories
745,971 files (21,214.26 mb)
2 Database/Transaction Logs (4.625 mb)
28,375.25 mb written to media
Elapsed time: 3h 7m 5s
Averagae Throughput 151.57 mb/min
*********************************

So this is telling me that there is just not enough room on those tapes or compression is not working properly.. Thing is, this is only 3 of our 5 servers, so now what? New and bigger tape drive?

[Robin Collins]

Hi Scott

Like you I've been to hell and back with Arcserve following upgrade from NT4 to W2K.

If you're running Arcserve 2000 then you need to have Active Directory and Win2k 'domain' controllers for it to behave - weird security mode they built in! I've had to go back to NT4 for the Arcserve boxes 'cos I just do not have the time or resources to switch over to an AD forest.

If you have Antivirus on your backup machine you may want to consider switching it off - I got around 60% speed increase that way.

Compression under Arcserve is very variable and puts a big time overhead for little benefit. I normally get about 1.3 using hardware compression and 1.8 using software but oh boy does it add to the time. However that's with 1.5 million small files, YMMV.

Backup over the network can be very variable with Arcserve - in the end I've put my backup drives onto an old server with 100gb storeage. I then use MS robocopy to mirror the stuff I want to back up onto that machine. This reduces the hit on the network as robobcopy does incremental copy, normally takes about an hour to top up a 65gb mirror. tape drive can then get max thruput on SCSI

I'd suggest you let Win2K compress the folders you are backing up, and just use hardware compression in Arcserve.

Hope this helps a bit

Robin

[Scott_186]

Thanks Robin

When you say let win2k compress the folders itself, do you mean myself compress them or is that an option I have to turn on somewhere?? Arcserve isn't doing any compression right now, it's all hardware, if there is any there anyway..doesn't seem like it..

[Dave Dewar]

Hi Scott,

Looks like Robin has addressed your Arcserve issues.

About compression, do not use multiple compression methods on the same data. Choose one and use only that method. Otherwise you will get data expansion.

Software compression under windows will typically give you a better compression ratio than the hardware compression algorithm in DDS drives. However, you need a server that is fast enough to compress the data as well as sending it to the drive. You should expect to see about a 1.4-1.8 compression ratio for typical user file system backup.

Robin's suggestion about getting all of the data together on the backup server first and then sending it to the tape drive afterwards is a good idea. This is how high end systems work.

Arcserve supports tape spanning, however, if it is unattended backup you want then this is not much use to you unless you have an autoloader.

HP has just released the HP DAT72 product that stores 36GB native, 72GB at 2:1 compression so you could go out and buy this drive.

Cheers,

Dave Dewar

[Scott_186]

Thanks Dave

I think getting all the data on the backup machine before writing to tape, is not gonna happen.. I don't have near enough space available.. Anyway, same results as the night before, it backed up 28 gig and then asked for a new tape.. Either hardware compression is not working or the tapes i'm using are not what they say they are..

I'm using 4mm tape.. that's about all I see, except for the 4 up in the right hand corner.. that should be a 40 gig compressed right?