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Is transferring data from an SSD to HDD and HDD to SSD speed about the same as HDD to HDD speed for both ways?

Falcon Momot
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penu
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  • how much research have you done on your own? This question right now is not very high quality – aaaaa says reinstate Monica Jan 08 '16 at 22:11
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    I researched with varying answers: some say that it's exactly the same, some say that the caching in the SSD makes it a bit faster for both ways, and some say that ssd to hhd is much faster than hdd to hdd – penu Jan 08 '16 at 22:13
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    How do I make this question less broad? It's as specific as I can make it. – penu Jan 08 '16 at 22:18
  • @penu You could start by specifying the type of transfer. Are we copying lots of small files? Are we copying one large file? You could specify filesystem or OS. You could specify specific SSDs or HDDs. – David Schwartz Jan 08 '16 at 22:26
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    @DavidSchwartz I didn't even know that it mattered small files vs big. Isn't this a hardware issue not software? Plus OS shouldn't matter, as I'm not asking how much faster, just IF it's faster. – penu Jan 08 '16 at 22:42
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    @penu It makes a huge difference. With lots of small files, HDD performance is dominated by seek time. With large files, HDD performance is dominated by transfer time. Whether OS or filesystem matters depends a lot on the specifics of the setup and at least knowing the OS, we'd know which questions to ask. – David Schwartz Jan 08 '16 at 22:48
  • @penu generally speaking, StackExchange designed to answer problem-solving questions. Your question right now is off-topic, due to rule http://serverfault.com/help/dont-ask "there is no actual problem to be solved". Define problem you are trying to solve, i.e. "I am looking for fastest way to transfer data from location A to location B, does it matter what hardware A and B running" – aaaaa says reinstate Monica Jan 08 '16 at 22:51
  • @aaaaaa sorry, I thought this was a Q&A site. Guess not – penu Jan 08 '16 at 22:57
  • @penu it is Q&A with somewhat defined scope – aaaaa says reinstate Monica Jan 08 '16 at 23:30

1 Answers1

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In the general case, the HDD will be the limiting factor for how fast that operation will go. In the specific case of doing a block copy from the HDD to the SSD, which is a 100% sequential operation, the HDD will keep up. If it is a file-copy, there will be enough jitter in the disk-access pattern that it will lag the SSD enough to be the limiting factor; this effect gets stronger the more randomized the data is on the HDD.

Going the SDD -> HDD route with a big file-copy, even that will suffer from randomization penalties on the HDD. File metadata operations will interrupt the sequentiality of the data being written; the more files, the bigger the hit.

sysadmin1138
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