Most tape formats detail the maximum native capacity (without compression) and the maximum compressed capacity. These figures are approximate maximum capacities for the tape drive and these maximums are got under great conditions.
Because real world systems rarely meet great conditions, you can be unable to achieve the specified maximums. For example, the kind of data you are attempting to compress has a great effect on capacity. Some types of data just don't compress well.
If you are seeing noticeably lower capacity, it may be due to a few of the following reasons:
The tape drive's information compression is not enabled. Tape drives that compress info use compression by default. But there are ways for tape drive compression to be turned off thru the backup application. Test your application to see if it has got a setting for hardware compression. In most cases, you will want to confirm hardware compression is turned on.
You could be writing data that does not compress well.Maximum capacities for tapes are customarily based primarily on a median 2:1 data compression ratio (or 2.5:1 for Exabyte M2 drives and some Sony AIT drives). Some sorts of data compress at a higher proportion; others compress at a lower ratio. For instance, executable files and graphics files typically don't compress well.
The tape drive might be trying to compress info that is already compressed.If your backup program compresses info before sending it to the tape drive, the tape drive can't compress it further. In reality the extra attempt at compression may cause the information to expand. Do not use both software and hardware information compression. If the tape drive is ready to compress info, switch off the software compression in your backup application.In the same way, compressed files on your hard disk will not compress any farther when fed thru the tape drive's hardware compression chip. If you are backing up a high proportion of already compressed files, such as MP3, AVI, and JPG files, then you won't see any farther compression at the tape drive level. Actually as the info is compressed twice, it may actually expand. Try turning off hardware compression and software compression in your backup application.
Your system may struggle to stay alongside of the tape drive.If your personal computer does not send information to the tape drive as speedily as the tape drive can write information to the tape, the tape drive stops and waits for the PC. Every time the tape drive stops, it writes gap tracks (tracks of undefined info) to help in repositioning when more data becomes available. If the tape drive has to stop and restart often, tape capacity is influenced. Check if there are transfer bottlenecks in your system. For instance, if you are backing up info over a 100bT network, a typical transfer rate could be far slower than you are expecting. In this situation, changing the network to at least 1GbE and for should improve both transfer rates and tape capacity. For the newest servers and LTO5 drives, a full 6Gb/sec should be supplied to the tape drive.
Your tape might be prepared for retirement.If you're using a tape that is well worn, the tape drive might be performing high numbers of rewrites to correct errors. Excessive rewrites scale back the tape's capacity. Try cleaning the tape drive with the right cleaning tape for your machine employing a new tape, and ensure you are using high quality information cartridges.
Your tape drive may need to be cleaned.An accretion of waste in the tape drive or on the recording heads can lead to increased error rates and rewrites. If you haven't cleaned your tape drive recently, try cleaning it with the appropriate Cleaning Cartridge for your tape drive model.
Because real world systems rarely meet great conditions, you can be unable to achieve the specified maximums. For example, the kind of data you are attempting to compress has a great effect on capacity. Some types of data just don't compress well.
If you are seeing noticeably lower capacity, it may be due to a few of the following reasons:
The tape drive's information compression is not enabled. Tape drives that compress info use compression by default. But there are ways for tape drive compression to be turned off thru the backup application. Test your application to see if it has got a setting for hardware compression. In most cases, you will want to confirm hardware compression is turned on.
You could be writing data that does not compress well.Maximum capacities for tapes are customarily based primarily on a median 2:1 data compression ratio (or 2.5:1 for Exabyte M2 drives and some Sony AIT drives). Some sorts of data compress at a higher proportion; others compress at a lower ratio. For instance, executable files and graphics files typically don't compress well.
The tape drive might be trying to compress info that is already compressed.If your backup program compresses info before sending it to the tape drive, the tape drive can't compress it further. In reality the extra attempt at compression may cause the information to expand. Do not use both software and hardware information compression. If the tape drive is ready to compress info, switch off the software compression in your backup application.In the same way, compressed files on your hard disk will not compress any farther when fed thru the tape drive's hardware compression chip. If you are backing up a high proportion of already compressed files, such as MP3, AVI, and JPG files, then you won't see any farther compression at the tape drive level. Actually as the info is compressed twice, it may actually expand. Try turning off hardware compression and software compression in your backup application.
Your system may struggle to stay alongside of the tape drive.If your personal computer does not send information to the tape drive as speedily as the tape drive can write information to the tape, the tape drive stops and waits for the PC. Every time the tape drive stops, it writes gap tracks (tracks of undefined info) to help in repositioning when more data becomes available. If the tape drive has to stop and restart often, tape capacity is influenced. Check if there are transfer bottlenecks in your system. For instance, if you are backing up info over a 100bT network, a typical transfer rate could be far slower than you are expecting. In this situation, changing the network to at least 1GbE and for should improve both transfer rates and tape capacity. For the newest servers and LTO5 drives, a full 6Gb/sec should be supplied to the tape drive.
Your tape might be prepared for retirement.If you're using a tape that is well worn, the tape drive might be performing high numbers of rewrites to correct errors. Excessive rewrites scale back the tape's capacity. Try cleaning the tape drive with the right cleaning tape for your machine employing a new tape, and ensure you are using high quality information cartridges.
Your tape drive may need to be cleaned.An accretion of waste in the tape drive or on the recording heads can lead to increased error rates and rewrites. If you haven't cleaned your tape drive recently, try cleaning it with the appropriate Cleaning Cartridge for your tape drive model.
About the Author:
The writer is a lto repair expert running a local business concentrating on lto repairs and network attached storage.
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