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SSD caching with striping possible ?

Posted: Mon Mar 15, 2021 12:30 pm
by wchris

I have an old board with a SATA2 controller :wtf: .

Upgrading the board with a Sata3 SSD limits me to Sata2 3BG bandwith (in reality only 2.5BG).

But the controller can handle 4 Sata2 ports

if I could use a small ssd to cache the big one with striping (like in raid) I could reach on two ports 5GB bandwith :idea:

Is striping technology pĂ´ssible with primocache ? if yes Did you make tests and would it increase the main SSD performance to read on two lanes ?

a bit like dual channel rams, if it improves ram why not SSD ?

My example is with an old sata2 board, but maybe it could also increase ssd throughput on newer sata3 ?

if on sata port 1 I have the main SSD "A", on port 2 I have a small SSD "B1", an on port 3 I have another small SSD "B2"
Bloc 1 and 4 are read from main SSD "A", bloc 2 and 5 are read from SSD cache "B1", bloc 3 and 6 are read from SSD cache "B2", etc ..
each cache only storing blocks required by his stripping setup. (But unlike raid it's still a cache and SSD "A" still holds all the data)

Re: SSD caching with striping possible ?

Posted: Mon Mar 15, 2021 5:26 pm
by Jaga
If the drives (group of striped target disks) are recognized by the OS at boot time, they can be used by Primocache as a cache volume without problems. Plenty of people have used RAID 0 for example to combine SSDs into a larger L2 target.

I'm not sure if you are using an actual RAID architecture, whether or not that is RAID 0, 1 or 0+1. Or if your controller has some proprietary striping technology. It was hard to determine this just reading what was posted. But again - if the OS recognizes it at boot time, then Primocache should be able to use the volume.

Re: SSD caching with striping possible ?

Posted: Sun Mar 21, 2021 12:45 pm
by wchris
Hello Jaga,

Thank you for the answer, maybe I was wrong and stripping is not the right name for the feature.
With raid 0 you aggregate the space to get a bigger logical disk.
with raid 1 you mirror the data to get backup and speed increase.

But with raid 1 you need a second disk with the same space and it's a big waste of space. The bigger the disk, the bigger the waste.

With a cache you can use a smaller second SSD and waste less space.
By caching only 1/2 or 1/3 of blocks you should aggregate throutput and get speed increase.

Also it's much easyer to setup and remove that a raid ! Primoche is so easy to use.

Of course this is theorical and has to be tested in real world configuration to see if it makes sense and gains are enought.