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Long-Term Storage of Moderately Large Datasets?
hawkeyeMI writes "I have a small scientific services company, and we end up generating fairly large datasets (2-3 TB) for each customer. We don't have to ship all of that, but we do need to keep some compressed archives. The best I can come up with right now is to buy some large hard drives, use software RAID in linux to make a RAID5 set out of them, and store them in a safe deposit box. I feel like there must be a better way for a small business, but despite some research into Blu-ray, I've not been able to find a good, cost-effective alternative. A tape library would be impractical at the present time. What do you recommend?"
I don't think you can beat a bunch of conventional hard disks in a RAID5 for both cost-per-TB and backup/restore performance, not to mention medium-term data integrity. Might be able to make hooking up the drives more convenient with an eSATA mult-bay enclosure, but those are kinda expensive. But I bet your backup box already has some sort of hot-swap on it already, like: http://www.amazon.com/Thermaltake-BlacX-eSATA-Docking-Station/dp/B001A4HAFS
I assume you already compress your data, since scientific datasets tend to compress well. You might consider compressing to squashfs, since it will let you do transparent decompression later on so you can skip the restore step if you just need a handful of files.
And optar:
http://ronja.twibright.com/optar/
You know it makes sense.
Deleted
It might not be the cheapest option, but with Amazon's AWS, you can snail mail them a copy of the drive with the data and they're store it in S3 storage buckets.
Hard drives are ridiculously cheap these days, especially for how much data you are storing. You may wish to consider buying drives from different manufacturers but of the same size to put in a single mirrored set. This way if there is a problem with a particular batch of drives it won't ruin everything.
LTO tape, properly stored, will outlast burned optical media and hard drives. Great stuff and designed specifically for what you're talking about.
http://en.wikipedia.org/wiki/Linear_Tape-Open
Learning HOW to think is more important than learning WHAT to think.
It can get a little pricey for huge datasets, but Amazon S3 now has an option where you can ship your data on a big set of disks directly to them, they will import everything into S3, and it will live there forever. The nice thing about S3 is unlike physical disks, it can grow essentially forever, and comes with retention and redundancy guarantees. And once your stuff is in S3, you can recycle the same disks to mail them more data.
With the advent of 2TB drives, you could easily combine 3 of these with software RAID 5 as you suggested. Depending on how long you need to keep the data, recording them to dual-layer blu-ray disks might be a better solution. Ya, it's a lot of disks (you can buy 100GB discs now), but they'll last longer and you don't have to worry so much about mechanical failure or needing a certain OS when you want to restore them.
Sabre
You might look at a www.drobo.com as a set of 4,5 and 8 drive enclosures. 1 TB disks gives you 3 TB usable space with a 2 drive failure tolerance. I have the older 4 bay drobo (2 for myself, and 2 at separate clients offices). It is much simpler to use, and will scale to your 2-3tb use and allow mismatched drives that normal raid will not use. Get a enclosure to start with, and then financing permitting, get a 2nd for Drobo redundancy. Not the fastest or cheapest, but reasonably good by both accounts, and simple to use.
Because Amazon can be *expensive* compared to doing it yourself ($$$ for data in, $$$ for data out, $$$ for monthly storage). But heh, what do I know. I just manage the storage for one of the LHC detectors (5PB spinning disk, 17PB tape). Amazon is good when you've got VC money or have no IT folks.
Label it something like complete american idol blueray collection and upload it on p2p to piratebay. every couple years rename it to some other horrible popular tv series. It will be self sustaining form of storage with infinite number of redundant hosts.
I would use RAID6 not RAID5, since 2 drive failures means data loss with RAID5, while it takes 3 drive failures to loose data on RAID6.
Linux MDADM has supported RAID6 for years, it's stable.
I would mix and match drives, not buying all the same model from one maker. One Samsung, One WD, One Hitachi, One Seagate.
That gets you 4TB in 4 drives, and unlike a RAID1, any 2 drives can fail with no dataloss.
You can further ensure no dataloss by making a second copy using different brand drives for each clone.
Eight 2TB drives is around $1500. Not bad for a very safe 4TB backup.
you make the assertion that a tape archive would be impractical, but really it is the most practical solution. the drive will set you back a couple thousand, but 800 gig tapes are only around 40 bucks each, and they are engineered for data storage unlike hard drives. this will only cost $160 per 3 gig dataset, or 200 if you use par2 files and an extra tape to make it recoverable in case a tape does fail.
Snowden and Manning are heroes.
Ok, yes, we see you know a lot about this.
So what's your recommendation?
Huh, don't you see has has Too Much to Do?
Tape is probably your best option. You can buy at DAT-5 (or even a DAT-4) tape drive for not very much. The tapes cost about $10 to $30 each (depending on what tape option you choose). Make 3 copies of the data set, store one onsite, store another offsite in a secure/climate controlled facility and send the 3rd to the client. Buy a spare tape drive and use both to make writing across tapes easier. There is a wide variety of software to write to the tape; we use the aging Retrospect.
The disk options is just way too complex; if anything, skip the RAID option and just store 2 copies. Putting the RAID sets back together and finding the RAID software will be nearly impossible in a couple of years. Use some standard formatting on the drives (FAT, NTFS, etc.) and you'll be good to go for the next 15 years.
Repeat never use DVDs as long term storage. I have seen them go unreadable anywhere from 2-5 years. I have fired up disk drives 10 years later with no problems. They are cheap reliable and fast. Don't try and get fancy just compress and store data sets over multiple volumes. Don't use RAID.
That's what ZFS is for.
mount -t gmailfs /disk1 -o username=gmailuser,password=gmailpass /disk2 -o username=gmailuser,password=gmailpass /disk3 -o username=gmailuser,password=gmailpass /disk4 -o username=gmailuser,password=gmailpass /disk5 -o username=gmailuser,password=gmailpass
mount -t gmailfs
mount -t gmailfs
mount -t gmailfs
mount -t gmailfs
zpool create gzfs raidz1 disk1 disk2 disk3 disk4 disk5
Actually.... I think I just found my project for the evening. I mean it's already been done with 12 USB drives
I work as a contractor for the USGS and the projects I've been involved with host, archive and provide means for customers to access all our different satellite data products. We've got a Long-term archive method for tons of data products (digitally and tangible) and I can honestly tell you the first thing that always comes up is: how often will the data need to be accessed?
For the longest time (almost a decade) we used 3 big, STK tape silos for data archive and retrieval for custom orders. The problem behind that type of design is we used a archive in a completely wrong manner in the fact that we tried to use it as a archive and a quasi-online retrieval system into a caching filesystem. We had tape mount counts in the hundreds and thousands, constant mechanical tape issues because of the excessive use, ect. We actually decided to move it all to online storage using enterprise RAID (EMC Clarion) and moved to a small LTO-4 tape unit for almost permanent, maybe-once-in-a-great-while storage and the rest we leave completely on spinning disk and control the access to it via application layer network protocols as needed.
IMHO, I really think it's going to depend on the access frequency of your data. If that custom needs their data once, and maybe never again in case they lose it, put it on tape. If it's a requirement they can get the data from you any time they want and you've got the hardware and administrative resources, power and bandwidth, put it some RAID.
Feel free to ask more questions.
Almost forgot to add. Never pay for expensive disk systems. Put the intelligence into your application instead. It'll scale faster and much cheaper. You also aren't locked into a technology (and instead, can enjoy the falling costs of storage, both spinning and SSD).
A problem I have here is the definition of 'long term'. To each of us it means something different.
In my job I have to archive 1.6 terabytes of data per day, and keep it around for 45 days (which, BTW, is not my definition of LONG TERM). For this task I utilize Data Domain storage, which utilizes data deduplication techniques for massive compression.
What you find is that at the block level your data may in fact be incredibly deduplicatable. In my case it very much the situation. I am currently storing 86 terabytes of rolling archives within 2.5 terabytes of physical disk space.
The problem with any technology you use for 'long term' storage is the ability to read those archives later. Assuming the media doesn't self degrade inside of the time frame you call 'long term', you must have the tools to read that media again. If you use BluRay, then you must store a compatible drive with it. (Nothing says Sony will not change the standard in two years and make all current drives obsolete, so no one makes them any more). Tape is worse, in that in two major model revisions, drives wont be able to read your media because its density is to low for the new drive head technology. Hardware based disk raid has the issue that the controller the raid was built with needs to stay with that raid. Another controller from the same manufacture, with the same model number, but a different firmware revision may not be able to figure out the raid, and declare the drives empty. Software raid is a little easier to deal with as long as you keep a copy of the OS you used to create it with in the same box. But then, during your defined 'long term' period, will you still have access to a system you can even plug these drives into, or run the OS on?
What you end up dealing with in reality is that as an archivist, you either ignore these facts, or you invest in a constant media / technology refresh and spend large amounts of time keeping your archives on the latest storage available.
Of course, all this falls apart if your definition of 'long term' isn't as long as some will project. In my case, my archives roll over every 45 days. I could easily keep that data alive for years on a live piece of hardware with a service contract. If I do not trust that hardware enough, I can buy two and replicate between them. (which, actually I am, for disaster recovery purposes)
With deduplication my (acknowledged) high initial investment quickly outweighs the cost of single purpose drives holding one copy, and wasting unused space. My purchase cost was less then $60k, but if I had to store all of that data in its raw form, my costs would be in the millions. However, if the data is not deduplicatable, then of course it is a moot point.
Each answer has it flaws. You decide which risks are acceptable, plan your best to deal with obsolesce, and define your definition of 'long term'. You also have to be ready to change your solution, when the one you choose today, fails to be the right solution for your needs in 5 years.