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

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ari2asem

Active Member
Dec 26, 2018
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The Netherlands, Groningen
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

Radioactive Member
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

New Member
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

Active Member
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

Active Member
Dec 26, 2018
745
128
43
The Netherlands, Groningen
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

Active Member
Dec 26, 2018
745
128
43
The Netherlands, Groningen
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