Shrinking the SD card occupancy

Of course that is not a property of RAID-1 but only of a dumb implementation of RAID-1. There is no reason whatsoever why a request to read 128MB of data could not be satisfied by reading 64MB from one and 64MB from the other drive. After all, both drives have the same data and can operate in parallel.

That the developers do not want to do it does not mean it can't be done, and indeed it is done by certain hardware-based raid controllers.

Reply to
Rob
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On the pi I see a limit of I/O at around 21 MB/sec (that is 21 megaBYTES per second, or ca 165 megaBIT per second). This seems to be due to the interrupt handling capacity of the device.

On my laptop with it's very fancy SSD disk I see 450 MB/sec with the very same linux version. But that is just what hardware gives you.

The two USB disks(like, rotating rust) I have connected to the pi give around 4.5 MB/sec read speed. Which is probably what the devices themselves can handle, they ARE cheap devices.

The differences between 1k and 1m block size on the pi was 19.9 vs 21.1 MB/sec. Linux does the job, obviously; just have to run more I/O requests through.

When running the 117 MB file the second time (all from cache) it gave an I/O rate of 64 MB/sec.

-- mrr

Reply to
Morten Reistad

Actually, on second look, the smaller block sizes did use a little more CPU. But then there's just so unbelievably much CPU to burn on a reasonably modern PC doing a simple task...

Reply to
Anssi Saari

yes. In the end its not the issue it used to be. setting up the call do wrote one byte is a lot less than actually writing it these days. It wasn't ALWAYS the case though.

--
Ineptocracy 

(in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
Reply to
The Natural Philosopher

Indeed. In fact I think when I set up a Linux RAID-1 about ten years ago on Red Hat Enterprise Linux 3 I did get double the read speed on RAID-1. Can't really be sure, it's been so long. But certainly I'm not getting double speed reads now, in fact my little Linux RAID-1 file server provides the speed of the slower disk during reads. (Disks are actually identical, the "slower" disk is just connected to a slower controller.)

Reply to
Anssi Saari

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