Stream Data Directly to External Hard Drive

[[email protected]]

Hello, I was wondering if anyone knew of a company that makes external
hard disks with an integrated real-time port that allows you to store
data directly to the hard disk and the external hard disk would have
some connection to a computer either parallel or USB. I'm looking for a
solution to capture 32-bits of data at a rate of 20Mhz and a co-worker
mentioned that a long time ago he used something similar to an external
hard disk with a real-time port. I was looking for solution that could
capture the data without the need for a computer, but could connect to
a computer after the data has been collected.

Thanks,
joe

 

[Keith Williams]

Hello, I was wondering if anyone knew of a company that makes external
hard disks with an integrated real-time port that allows you to store
data directly to the hard disk and the external hard disk would have
some connection to a computer either parallel or USB. I'm looking for a
solution to capture 32-bits of data at a rate of 20Mhz and a co-worker
mentioned that a long time ago he used something similar to an external
hard disk with a real-time port. I was looking for solution that could
capture the data without the need for a computer, but could connect to
a computer after the data has been collected.

80MB/s may be pushing the envelope a bit for today's disk drives,
but may be possible with a RAID setup. You're going to need
something in there to take care of the file system so the PC can
read the data. The above sorta points to a PCish sort of embedded
thing. How much data do you need to record? What price point?

 

[[email protected]]

Hello, thanks for responding to my post. I would like to capture
20-mintues or more. I guess our price budget would be near $50K.

thanks,
joe

 

[[email protected]]

80MB/s may be pushing the envelope a bit for today's disk drives,
but may be possible with a RAID setup. You're going to need
something in there to take care of the file system so the PC can
read the data. The above sorta points to a PCish sort of embedded
thing. How much data do you need to record? What price point?

Speed issue noted, but you don't need a file system, or at least more
than a very degenerate one.

A file system is usefull when you want to organize you disk and not
simply treat it like a tape drive. In this application, treating like
a tape drive may be fine - you just start at the first sector of the
LBA and write as many as you feel like. Okay, it might be nice to know
how many your wrote, and optionally set the starting address, but there
are ways of doing that without making a design go much beyond a state
machine in an FPGA.

But given that the next post offers a fairly high budget, a RAID array
in a server class PC, or several PC's sharing the load, may make sense.
It might be possible to develop custom logic far below that price, but
unless they need a lot of them or it's compelling as a design challenge
there's not much point.

 

[Keith Williams]

Speed issue noted, but you don't need a file system, or at least more
than a very degenerate one.

True, but a nonstandard filesystem is going to make reading the
disk a tad more complicated. OTOH, a nonstandard filesystem may be
required to get the speed.

I was thinking about disk drive's STR and 90MB/s is about the best
on the market today for average STR. However, that is an average
and it falls off towards the center. Another problem is that STR
is *read* performance. Writes are a different kettle and sustained
write speed isn't often specified. There are other issues with
writes being committed and such. ...could get sticky.

A file system is usefull when you want to organize you disk and not
simply treat it like a tape drive. In this application, treating like
a tape drive may be fine - you just start at the first sector of the
LBA and write as many as you feel like. Okay, it might be nice to know
how many your wrote, and optionally set the starting address, but there
are ways of doing that without making a design go much beyond a state
machine in an FPGA.

True, but a FS makes operating on the data a little easier. I
doubt there he needs *all* 96GB per go. If the OP does, capturing
the data is only the start of the headaches. ;-)

But given that the next post offers a fairly high budget, a RAID array
in a server class PC, or several PC's sharing the load, may make sense.

Even a PC is kinda tight. 20MHz (80MHz) on the PCI bus is kinda
iffy. Double that and it's... Synchronizing several PCs sounds
difficult too.

It might be possible to develop custom logic far below that price, but
unless they need a lot of them or it's compelling as a design challenge
there's not much point.

I did a similar thing, on a different scale, 20 years ago. I built
a "logic analyzer" to capture all of the I/O on microprocessors (or
peripheral chips). The intention was to capture interesting events
from a system and translate them into a test program for a logic
test system. The hardware ended up being 128bits wide and 1Mb deep
at up to 50MHz (or 256b x .5mb at 25MHz). As you say, it was an
interesting challenge and I had a boss with deep pockets. ;-) The
hardware alone was over $50K (even with a free source of DRAM).

 

[Keith Williams]

Hello, thanks for responding to my post. I would like to capture
20-mintues or more. I guess our price budget would be near $50K.

Twenty minutes is about 96GB so you're not going to get away with
using only the outside zone of a single disk. Splitting the data
into a couple of streams shouldn't be too hard and 40MB/s should be
relatively easy with a fast/modern drive. The hardware should be
simple, but $50K doesn't allow much for engineering.