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I'm in the process of setting up my home network, and since I'm planning on having a backup/file server and doing backups to it over SSH, I'd like to get a scope on the speed of transfer and what I can hope to achieve transferring locally across my home network (so no real bandwidth concerns as far as uplink and downlink speed).

What are some realistic speeds I can expect for the following scenarios:

  1. Laptop backing up over WiFi, has a wireless-n capable card. I can connect this computer to my 5GHz channel if that makes a big difference.
  2. Laptop backing up over a CAT-6 cable.
  3. Laptop backing up directly to an external hard drive over USB 2.
  4. Local machine backing up directly to hard disks over SATA 2.
  5. Local machine backing up directly to hard disks over SATA 3.

The typical use-case will be #1, but I'd like to familiarize myself with what these different methods can achieve, so I can make the right choice when backing up. If need be, I can elaborate.

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4 Answers

up vote 3 down vote accepted
  • wireless-n can give you 300 Mbps,

  • for CAT-6 you can get a theoretical 1 Gbps

  • USB 2 gives a theoretical 480 Mbps (most high speed drives cannot do more than 200 though)

  • SATA 2 gives 3 Gbps

  • SATA 3 gives 6 Gbps

Its really all about the lowest common denominator. If you are a running a CAT-6 to an old drive that can write at 20 Mbps, nothing will get you above that. As a rule, you will almost never get the speeds listed above, unless you have very good hardware (last two are possible with solid state drives though). Always better to be right there (locally plugged in) as a rule though.

You might find that a defrag will go a long way (though not on ext3 or ext4 filesystems which are much less prone to fragmentation than NTFS) to increasing your speed regardless of the transfer medium as your drive will a lesser seek time, and even a slightly smaller amount over large amounts of data adds up.

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Defrag. Even when running ext4? ;) Thanks for the response. –  Naftuli Tzvi Kay May 26 '11 at 1:25
    
I don't know much about ext4 specifically, but I would from some cursory reading that all file systems are prone to fragmentation, and that it would still help. I could not tell you how much though. As a generally rule, unless you are using an SSD (Solid State Drive) its a good idea to defrag once every few months or so. –  soandos May 26 '11 at 1:27
    
Downvoter care to comment? –  soandos May 26 '11 at 3:43
    
Tools like e4defrag exist to defragment ext4 filesystems, but I would be very surprised if it made any noticeable difference. Even on ext3 defragmentation is a fairly unnecessary procedure. –  user55325 May 26 '11 at 3:50
1  
What makes the ext4 filesystem so resilient to fragmentation? –  soandos May 26 '11 at 3:51
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Even though the article I am linking is three years old and discusses Time Capsule, the analysis has proven to be good in my experience even as chipsets get better and new protocols come into play. 3 GB Sata, ThunderBolt, USB 3.0 are all going to be faster than most servers / disk spindles so you can still plan safely based on these numbers. Using a 5Ghz channel makes a huge difference for my backup speeds and reliability, so I would certainly configure that if you can.

Kudos to Apple Insider for putting this comparison of speeds together.

enter image description here http://www.appleinsider.com/articles/08/03/28/exploring_time_capsule_theoretical_speed_vs_practical_throughput.html

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Not everything you're asking about, but a start ...

"NAS vs eSATA vs USB vs Firewire vs 10/100/1000"

http://www.pcqanda.com/dc/dcboard.php?az=show_topic&forum=2&topic_id=526550

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WiFi is likely to be slowest (but not necessarily, since USB speed depends on a number of things - CPU load, drive type, other USB devices on the bus, etc.)

Cat 6 cable can support transfer speeds up to 10 Gbps in theory, but you'd have to have unusual, expensive, ten-gigabit network hardware to see those speeds. In reality you might well be limited to 100 Mbps, which is slower than direct SATA access. SATA 2 provides more bandwidth than most drives use today, except for fast SSDs. SATA 3 at 6 GB/s transferring to a high-end SSD is going to be faster than anything else, but this is an unlikely scenario for backups.

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