by Josefine.Fouarge, on Apr 28, 2015 7:28:58 AM
If you have read part I of Tape is dead! Long live the tape! you already know more about the differences between speed and performance regarding tape and disk devices. Section 3 'Tape is expensive' started with a calculation to figure out whether or not this myth is true.
3) Tape is expensive (continued)
A simple PowerVault MD3800i would fit the requirements. A sample configuration of a PowerVault MD3800i, with 12 4TB near line SAS drives will give right around that 32TB usable space depending on your configuration. This will also cost you about $18,000 with a decent discount, and if you can talk your sales representative into it maybe knock another couple of thousand off it. After all you still don’t know what kind of speed you will realistically get to the device (see 2).
Now let’s take a look at what Dell can do for us tape library wise. The PowerVault TL2000 Tape Library, 2U, 24 Slot, 1 drive with a 20 pack of LTO 6 media and labels will be sufficient. That is less than $10,000, and I know that I can get up to 160MB/s uncompressed speeds going to it.
With both configurations I didn’t add any fancy cables, software or warranty extensions, and neither extra discounts besides the regular one.
And now our data increases by 500GB, so we have to add storage space:
1,5TB for monthly full, 1,5TB for weekly full, and a couple of GB for differential/ incremental backups
New disk:
4TB 7.2K RPM Self-Encrypting Near-Line SAS 6Gbps 3.5in Hot-plug Hard Drive,FIPS140-2 [$836.85] --> but the PowerVault MD3800i has only 12 units, so actually we would need to buy a new storage system
New tape:
2x LTO-6Media1PK [ea. $69.57] --> $139.14
When buying a new storage device the SAN storage is at least $6000 more expensive than the tape library. Buying new tapes compared to buying new disks is substantially cheaper.
To take another angle into account, tapes are more cost effective energy wise. Using tape libraries as backup medium for less frequently used data, results in a reduction in energy consumption. A tape library of course consumes power too, but requires much less in the way of cooling. Their storage […] is offline, meaning energy-neutral.’ A disk instead is spinning all the time, thus is not only requiring energy all the time, but also needs to be cooled more than a tape.
4) Tapes are not reliable and die young
Before I start talking about which solution is most reliable, I’d like to mention: Both in combination!
I already mentioned the review of privacy and retention policies. One part of this review is the offsite data protection. Backing up to a tape and personally put the tape in a safe, is less threatening then sending business critical data through a maybe unsecured line to a server who knows where. Backup to disk to tape helps improving the sense of security.
In section 2 I talked about the difference between disk and tape speed-wise and mentioned that disk is faster when restoring single files and tape is faster when restoring a complete system. That is exactly the reason why backup to disk to tape is one of the most successful and most reliable backup strategies in data centers worldwide. The combination of both devices is the perfect way to keep business critical data save and to have a reliable and fast restore in a disaster.
But to finally defend the reliability of the tape, I found an interesting case study from NERSC:
“During this massive migration process, Hick and his team observed the center’s actual tape data reliability within its Active Archive. The findings flew in the face of conventional wisdom: 99.9991 percent of tapes were 100 percent readable, representing a 0.00009 percent error rate. Of the more than 40,000 tapes that were read, only 35 contained some data that couldn’t be accessed.”
Have you ever seen an error rate like that with disk systems?
With great reliability comes a long life, somehow. Several independent tests state that tapes can survive up to 30 years. It all depends on the usage and the type of tape. A tape used for a monthly retention will of course live a lot longer than a tape used for weekly retention. It is much harder to find accurate information about the disk as there are basically no long term studies. Backblaze is the one resource that is seems everybody refers to: “For the first 1.5 years, drives fail at 5.1% per year. For the next 1.5 years, drives fail LESS, at about 1.4% per year. After 3 years though, failures rates skyrocket to 11.8% per year.”
5) Hard to manage
Maintaining either device can bring some challenges. When you are a small business with just a few GB of data, both a SAN and a tape library are way too complicated. But there are single tapes and NAS storage devices that are easier to setup and to handle. You won’t have authentication complications with a tape device, but more likely will with a NAS.
Honestly, it is hard to compare these two. Both have their advantages and disadvantages. It really depends on the environment and on the use case. Some IT administrators have more experience with tape libraries, because they have used them their entire life. And others know exactly how to troubleshoot a SAN storage. It’s like being a Linux user that has to work on a Windows PC.
A tape is small and light, a disk not so much. E.g. dropping a tape doesn’t harm it. When you drop a disk, your data may be corrupted after ‘landing’. Changing a tape in a single tape drive or a tape library is do-able. Replacing a disk in a NAS or SAN can cause all sorts of headaches depending on how the NAS or SAN is configured.
I could go on with more arguments why a tape is the better choice (from the physical handling), but that will end nowhere. From a disaster recovery perspective a quote that I have always loved is ‘Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.’ Everybody has their preferences, but don’t discount the value of tape just because it is ‘old technology’.
So no matter how you like to back up your data (disk, tape, a remote location or just everywhere), NovaStor DataCenter helps keeping your data safe.
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