transfer rate calculations

[suren424]

Hi,

while i was going through the below link , i got many doubts

http://www.symantec.com/business/support/index?page=content&id=HOWTO56053#id-SF0S0118919

Some Points from the link :

Ideal transfer rate (data/(backup window),backup window=8hrs

Actual data transfer rate = (Amount of data to back up)/ ((Number of drives) * (Tape drive transfer rate)).

We use a LTO-4 tape drive in our environment.based on the below table and the examples from the link i did some calculations for the backup jobs we are performing now.

Drive	Megabytes per second	Gigabytes per hour, no compression	Gigabytes per hour, at 60% utilization	Gigabytes per hour, at 2:1 compression and 60% utilization
LTO-4	120	432	259.2	518.4

Amount of data to backup (full backup) -- 230 GB

Daily backup window = 8 hours

number of drives = 1

tape drive transfer rate : 518.4 

Actual data trasfer rate = 230/((1)*(518.4)) =0.4436728

With a data transfer rate of either 259.8 or 518.4 gigabytes per hour, a single LTO-4 tape drive easily performs the 230-gigabyte backup in less than 8 hours.

questions :

what is the backup window and how to decide one ?

In our case for 230GB of full backup it's taking 6hrs 10 min with job rate=619MB/min.

Could you please help me understand the above calculations.

Thanks

[pkh · Accepted solution]

The backup window is the time when you can do your backups.  Backups may affect other tasks/jobs and vice-versa.  Hence you would only do your backups during a quiet time when there are no other tasks/jobs running.  This is the backup Window.  For example, after your office closes at 5 p.m., you may be doing batch processing and/or housekeeping jobs until 9 p.m.  Hence you cannot start your backups until after 9 p.m. Your office opens at 9 a.m. in the morning and you don't want your backups to slow everybody down.  Hence your backups must complete by 9 a.m.  The period between 9 p.m. and 9 a.m. is your backup window.

Don't worry about the calculations.  These are theoretical calculations used to choose what backup technology you should use, so that you can buy the right equipment.  Obviously, if you have a 12 hour backup window, you cannot choose a technology which cannot backup the amount of data that you have within this 12 hours.

Since you managed to complete your backups within your backup window with your LTO4 tape, you are fine.

[suren424]

Thanks pkh .

We are preparing a backp policy and procedure document .based on that we can plan our jobs accordingly.

In that context,i wanted to understand the above calculations ,so that i can give some rough estimates on the job transfer rate and the amount of time it takes for each job to complete.

we have 1 LTO-4 drive and the max. backup job size we do is 230GB for now and the backup window available is 12 hours.

Help me in understanding those.

Thanks again.

[pkh]

Since you are already doing backups, you should use your actual backup times and not the theoretical numbers above.  Your actual backup times may be slower than the numbers above because there are other factors which can slow down your backup.  Theoretically, your 230GB backup should finish within 1 hour because in 1 hour at 60% utilisation, the LTO4 tape drive can handle 259GB, but your actual backup time may be slower than this.