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Support for shingled magnetic recording devices

Support for shingled magnetic recording devices

Posted Mar 29, 2014 19:15 UTC (Sat) by giraffedata (subscriber, #1954)
In reply to: Support for shingled magnetic recording devices by Cyberax
Parent article: Support for shingled magnetic recording devices

Well, tape is actually NOT cheaper unless you do it in a REALLY big way with tape libraries and robots.

Yes, that's what I was talking about. When I compare the economics of storage technologies, I think of large scale storage. With tape, there are thousands of cartridges and plenty of robots.

Even then it's only marginally cheaper than HDs.
The last figures I saw were 5x cheaper. That's total cost (not just e.g. purchase price of some box), and assuming a tape-friendly application. That seems perfectly believable to me, but if you know of a study showing otherwise, do tell.

So think about it - would you build a tape library with expensive robots and lots of tape or would you just prefer to buy somewhat slower hard drives?

I'm not sure what you're comparing here. Shingled disks aren't somewhat slower. Used right, they're the same speed as regular drives; used wrong, they're unusably slow. Since tape applications also work on shingled drives, the question would be, would you use something with 2 minute access time or just use slightly more expensive disk drives. Only since I'm claiming shingled drives are 4X more expensive than tape, that question is moot.

By the way, some of my data is on tape. My company backs up its general purpose filesystem to tape. It takes me 4 minutes to recover a lost file - 2 minutes to go through the interactive dialog and 2 minutes for the robots and tape drives to do their thing. Shingled disk would cut that to 2 minutes total. I can't imagine my company switching unless there is virtually no difference in the storage cost.


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Support for shingled magnetic recording devices

Posted Mar 29, 2014 20:32 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link]

> The last figures I saw were 5x cheaper. That's total cost (not just e.g. purchase price of some box), and assuming a tape-friendly application. That seems perfectly believable to me, but if you know of a study showing otherwise, do tell.
No way. The last time we checked (in 2013) the price difference was about 2x. The major advantage of tape was reliability - tape cartridges themselves contain no sensitive mechanic parts, not price.

LTO6 tapes are about $40 per tape (2.5Tb) when bought in bulk. Maybe $30 if you are really big. Hard drives are around $50 per 2Tb in bulk.

And that's without considering the cost of streamers (multiple $$$$), tape robots ($$$$$) and the storage software solution (shockingly, there are no good OpenSource hierarchical storage managers).

Of course, HDDs need some kind of SAN, but they are cheap these days. AoE/iSCSI solution for 1000 drives capable of 100Gb throughput can be bought for just under $30k and doesn't need any fancy software.

Support for shingled magnetic recording devices

Posted Mar 30, 2014 10:22 UTC (Sun) by khim (subscriber, #9252) [Link]

Shingled disks aren't somewhat slower. Used right, they're the same speed as regular drives; used wrong, they're unusably slow.

And when used with GFS or HDFS which need random read access to it's 64 megabytechunks and kinda streamlined write access to these chunks (GFS gives you the ability to append-write files, HDFS does not even offer that today) they are fast.

Shingled disks are only on horizon today, but API which is basically custom-taylored for their limitations is more than decade old and there are thousands of companies and millions of drives which are used for such kinds of applications. End of story.

Support for shingled magnetic recording devices

Posted Mar 30, 2014 16:34 UTC (Sun) by giraffedata (subscriber, #1954) [Link]

And when used with GFS or HDFS which need random read access to it's 64 megabyte chunks and kinda streamlined write access to these chunks (GFS gives you the ability to append-write files, HDFS does not even offer that today) they are fast.

I think those are two examples of things that would require re-engineering to work with shingled disks, because neither writes in log-structured fashion today. The only reason I can think of that an existing disk drive application would write in log-structured fashion (fill the drive, or a large segment of it, from beginning to end) is to maximize write speed. But GFS and HDFS assume there is little writing. HDFS is specifically aimed at fast sequential reading of large files, which means it needs to keep files contiguous on disk, which is not possible with a log structured file system.

Support for shingled magnetic recording devices

Posted Mar 31, 2014 10:36 UTC (Mon) by dlang (subscriber, #313) [Link]

I think that you wildly underestimate how expensive random writes are today, and how much software works to avoid them

I've seen a number of packages that have the pattern of having large chunks of data, but new data is not written directly to those large chunks, instead new data is written sequentially to an 'updates' file, and periodically some other job comes along and re-writes the large chunks to include the changes from the updates files, and then deletes the updates files.

such systems would be perfect for shingled drives, they would just get their chunk sizes and alignments adjusted to match.


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