purpose of cable 1 sff-8088 to 4 sff-8088

ari2asem

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Dec 26, 2018
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i saw this cable and i am wondering what de purpose of this cable

SAS Cable external SFF-8088 to 4x SFF-8088, 2m

does this mean that i can connect 4 jbod cases to 1 external sff-8088 port of hba card?

an example...jbod case has 16 hdd's and internally connected to internal ports of a sas expander (to sff-8087 ports). but this expander has also external sff-8088 port. so i connect 1 of those 4 cables to this external port of the expander. this setup multiplied 4 times and connected to 1 external port of a LSI 16e hba. thus in totally connecting 16hddx4cables/jbods cases = 64hdd's on 1 external port of a LSI 16e hba. and then this 64hdd multiplied 4x hba ports are 256hdd's in totall connected to 1 LSI 16e hba.

are my assumption right about usage of this cable?

another question...is sas2 protocol fast enough for playing 4k video from jbod case?
 

EffrafaxOfWug

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Feb 12, 2015
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another question...is sas2 protocol fast enough for playing 4k video from jbod case?
Depends what sort of video you're talking about.

Uncompressed 4K wouldn't work; 60fps 24bit 3840x2160 is ~11Gb/s, more than SAS2's 6Gb/s. More realistically I think common 4K compressed formats top out at ~250Mb/s and I've seen some sample footage at ~500Mb/s IIRC.

Compressed, you can usually fit 4K video coming off a blu ray (usually termed UHD rather than 4K) down a 100Mb pipe; the max bitrate is 128Mb/s but I've not seen it sustained.
 

ScootingCat

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Apr 17, 2015
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That cable splits out one SAS lane from the source device connector to each of the four "breakout" connectors. (see the PDF linked under the Downloads/Documents tab on that page)
I have no idea how or even if that would work with a SAS expander, but you'd only get one lane worth of bandwidth for each of the four connectors.

Edit to Add: One use case that comes to mind for that cable would be to connect four external SAS tape drives/libraries to a SAS HBA that only had one 8088 connector.
 

muhfugen

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Dec 5, 2016
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That cable is intended for uses like a tape library/autoloader, where you would have multiple tape drives and no expander or common connector available.
 

ari2asem

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Dec 26, 2018
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Depends what sort of video you're talking about.

Uncompressed 4K wouldn't work; 60fps 24bit 3840x2160 is ~11Gb/s, more than SAS2's 6Gb/s. More realistically I think common 4K compressed formats top out at ~250Mb/s and I've seen some sample footage at ~500Mb/s IIRC.

Compressed, you can usually fit 4K video coming off a blu ray (usually termed UHD rather than 4K) down a 100Mb pipe; the max bitrate is 128Mb/s but I've not seen it sustained.
just for information...i have done short and small test. playing 2 4k files at the same time from jbod-case. 4k 400mbit demo file (downloaded from jelly fish 4k sample website) w/o audio and a movie file with 4k 70mbit....and transfering data to jbod-case same hdd as playing off 4k file at around 105 MB/s (note: no mb, but MB)...this all at the same time and on the same hdd...
hardware: LSI 9201-16e connected with 5m sff-8088 cable to chenbro ck22803 expander inside jbod case...all 4k files play very nice, no hiccaps -:)
 

EffrafaxOfWug

Radioactive Member
Feb 12, 2015
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OK... so basically compressed, but at the limits of sensibility. Almost no-one has systems capable of playing back uncompressed 4k.

105MB/s makes it sound like you're bottlenecked on gigabit ethernet, assuming a sequential copy a modern HDD should be able to keep up with writing that and reading at 70Mb.

BTW I don't understand why people write mb when they mean MB. mb == millibit (one thousandth of a bit), which is a unit no-one uses because it makes no sense since a bit is as small as it gets in computing terms. MB == megabyte. Case matters!
 

ari2asem

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Dec 26, 2018
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105MB/s makes it sound like you're bottlenecked on gigabit ethernet, assuming a sequential copy a modern HDD should be able to keep up with writing that and reading at 70Mb.
where do you get the network part from? i didnt use any network. my jbod-case is directly connected to my host computer by sff-8088 ports / cables. so it is DAS, not NAS

i have should mentioned that my source disk during copying of files from it, was 2.5 inch 1TB. i think this is my bottleneck, being 2.5 inch disk which are not spinning that fast as 3.5 inch disks