Daniel Rozsnyó wrote:
James Richard Tyrer wrote:
I was considering buying a small 1-2 GByte flash disk form my system so
I was looking over what was available and didn't find what I wanted.
A system based on a CompactFlash memory card is very inexpensive.
However, I find that they are slower than a hard drive :-(.
The slowness is due to PIO mode, you might want to get a newer revision
ide-to-cf convertor, which has DMA support and an appropriate card.
So far I could only find them with DMA 0 which seems to be limited by
the card speed. DMA 0 is 16 MB/sec. The fastest CF (133x) is 20 MB/s.
SDs come slightly faster at 22.5 MB/sec which is still slower than DMA 1.
The inexpensive ones are based on the IDE/ATA interface and have a
socket for 1 CF card. It appears that not much is needed for this
interface.
Its only wiring :)
Perhaps some buffers. But DMA is going to need a DMA controller, isn't it?
I suppose that it might be relevant to know how wide the data bus on the
IDE and CF are. The IDE is 16 bit IIRC and IIUC CF flash is also 16
bit. So, it appears obvious to me that the speed could be increased by
using the PCI or PCIe interface and using several cards in parallel
(i.e. striping the data). With 32 bit PCI you could use 2 cards striped
in parallel and with 64 bit PCI you could use 4 cards striped in
parallel. It would also be possible to use 2 banks (or 2 disks) the
same as memory so that 32 bit could use 4 cards. Or, 2 disks with 2
banks each.
Since this idea is so obvious, I should probably patent it ASAP. :-D
It probably wouldn't need much besides a PCI controller to implement.
So, it is going to require a DMA controller and bus arbitration to be
really fast.
IIUC, CF cards come in different speeds and (obviously) the speed would
depend on the speed of the cards being used, but it looks like with fast
enough cards (133x?) a 64 bit PCI (or a 32 bit with 2 disks) could beat
SCII 160 or with 2 banks it could beat SCII 320.
This should considerably speed up a typical desktop Linux system if used
for swap.
Buy a 4 port USB adapter and put there 4 usb sticks and run RAID0 :) or
just 4 linux swaps (the kernel swaps to all of them in parallel).
Interesting idea. But is this really going to run 4x what one port would?
I'm currently using this on my diskless desktop (on onboard USB ports),
with 1x256MB and its quite slow when it cames to swap. But I have no
choice, coz it wont swap to file on NFS mount :/
So, basically, you would be a possible customer for this and you
wouldn't need one that could beat SCSI 160; you would find IDE DMA 2 an
improvement.
Perhaps SD cards are a better idea.
As stated above, they are available in 150x.
--
JRT
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