Back Up to Tape the Way You Shop For Groceries
- by rickramsey
Imagine if this was how you shopped for groceries:
From the end of the aisle sprint to the point where you reach the ketchup.
Pull a bottle from the shelf and yell at the top of your lungs, “Got it!”
Sprint back to the end of the aisle.
Start again and sprint down the same aisle to the mustard, pull a bottle from the shelf and again yell for the whole store to hear, “Got it!”
Sprint back to the end of the aisle.
Repeat this procedure for every item you need in the aisle.
Proceed to the next aisle and follow the same steps for the list of items you need from that aisle.
Sounds ridiculous, doesn’t it?
Not only is it horribly inefficient, it’s exhausting and can lead to wear out failures on your grocery cart, or worse, yourself. This is essentially how NetApp and some other applications write NDMP backups to tape. In the analogy, the ketchup and mustard are the files to be written, yelling “Got it!” is the equivalent of a sync mark at the end of a file, and the sprint back to the end of an aisle is the process most commonly called a “backhitch” where the drive has to back up on a tape to start writing again.
Writing to tape in this way results in very slow tape drive performance and imposes unnecessary wear on the tape drive and the media, especially when writing small files. The good news is not all tape drives behave this way when writing small files. Unlike midrange LTO drives, Oracle’s StorageTek T10000D tape drive is designed to handle this scenario efficiently.
The difference between the two drive types is that the T10000D drive gives you the ability to write files in a NetApp NDMP backup environment the way you would normally shop for groceries. With grocery shopping, you essentially stream through aisles picking up items as you go, and then after checking out, yell, “Got it!”, though you might do that last step silently. With the T10000D, it has a feature called the Tape Application Accelerator, which prevents the drive from having to stop after each file is written to notify NetApp or another application that the write was successful.
When enabled in the T10000D tape drive, Tape Application Accelerator causes the tape drive to respond to tape mark and file sync commands differently than when disabled:
A tape mark received by the tape drive is treated as a buffered tape mark.
A file sync received by the tape drive is treated as a no op command.
Since buffered tape marks and no op commands do not cause the tape drive to empty the contents of its buffer to tape and backhitch, the data is written to tape in significantly less time. Oracle has emulated NetApp environments with a number of different file sizes and found the following when comparing the T10000D with the Tape Application Accelerator enabled versus LTO6 tape drives.
Notice how the T10000D is not only monumentally faster, but also remarkably consistent? In addition, the writing of the 50 GB of files is done without a single backhitch. The LTO6 drive, meanwhile, will perform as many as 3,800 backhitches! At the end of writing the entire set of files, the T10000D tape drive reports back to the application, in this case NetApp, that the write was successful via a tape mark.
So if the Tape Application Accelerator dramatically improves performance and reliability, why wouldn’t you always have it enabled? The reason is because tape drive buffers are meant to be just temporary data repositories so in the event of a power loss, there could be data loss in certain environments for the files that resided in the buffer. Fortunately, we do have best practices depending on your environment to avoid this from happening. I highly recommend reading Maximizing Tape Performance with
StorageTek T10000 Tape Drives (pdf) to decide which best practice is right for you. The white paper also digs deeper into the benefits of the Tape Application Accelerator. The white paper is free, and after downloading it you can decide for yourself whether you want to yell “Got it!” out loud or just silently to yourself.
Customer Advisory Panel
One final link: Oracle has started up a Customer Advisory Panel program to collect feedback from customers on their current experiences with Oracle products, as well as desires for future product development. If you would like to participate in the program, go to this link at oracle.com.
photo taken on Idaho's Sacajewea Historic Biway by Rick Ramsey
- Brian Zents
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