Low cost SCSI ramdisk?

I am looking to find a low cost SCSI storage unit that is both very
fast, and has permanent store capabilities. I am envisioning a 1U box
that essentially is one big RAMDISK. And it has a battery and a hard
drive, so in the event of a power failure, all the data in the RAM
disk can be flushed to the hard drive. A gigabyte or two is all the
storage that I need for the RAMDISK. I have found Imperial Technology,
but their prices are way out of the range I am interested in.

-Jim

"Low cost", "SCSI", "RAM disk" and "very fast" is about as oxymoronic
as it gets. SCSI RAM disks have always been at the very high end of the
price scale since the market segment is very small. Figure the
engineering to put a SCSI frontend (with a couple of man-years worth of
firmware) on a RAM as small as 1 GB. We used to have RAM disks of that
size 6 or 8 years ago - at a couple grand each. Maybe you can find a
used one, but watch out for battery life. We used NiCd back then.

If you look closely at a RAM disk with integrated backup, it's a disk
drive with a UPS and a cache the same size as the disk. Implementing
this at the system level is easy. That's why there's only such a small
market - RAM disks are only needed if the system has special
requirements or constraints, e.g. legacy systems.

Ralf-Peter

On 29 Nov 2004 09:35:52 -0800, (Jim Wall) wrote:

I am looking to find a low cost SCSI storage unit that is both very
fast, and has permanent store capabilities. I am envisioning a 1U box
that essentially is one big RAMDISK. And it has a battery and a hard
drive, so in the event of a power failure, all the data in the RAM
disk can be flushed to the hard drive. A gigabyte or two is all the
storage that I need for the RAMDISK. I have found Imperial Technology,
but their prices are way out of the range I am interested in.

-Jim

For 4gb or under go with an nvram card on the host. Or put it in a
dedicated host, whatever.

MicroMemory has 4gb NVRAM cards that are battery backed. Fast as you
are gonna get, straight to memory. Not sure of costs but like
Ralf-Peter mentione, cheap is not going to be an option for what you
are asking.
I have not used their products but I have kept them in mind. I saw
them at a trade show and they had some interesting options unique to
them.

www.umem.com

~F

On 29 Nov 2004 09:35:52 -0800, (Jim Wall) wrote:

I am looking to find a low cost SCSI storage unit that is both very
fast, and has permanent store capabilities. I am envisioning a 1U box
that essentially is one big RAMDISK. And it has a battery and a hard
drive, so in the event of a power failure, all the data in the RAM
disk can be flushed to the hard drive. A gigabyte or two is all the
storage that I need for the RAMDISK. I have found Imperial Technology,
but their prices are way out of the range I am interested in.

Your problem will be the software. Sure, creating a (say) 2GB
ram-based storage thing that dumps to an HDD when a UPS says "No AC"
is not hard, but making that thing look like a parallel or FC SCSI
target is harder. Although making it look like an iSCSI target may be
a "solved problem".

I, being paranoid (and experienced) would go with two HDDs, not just
one, and use a system that periodically writes the RAM to alternating
HDDs, then updates a "generation" count on the disk. On shutdown, you
just have to copy the current image to the next disk to be safe, and
then copies it to other disk to be safer. Bootup becomes relatively
easy: if the generations match, you shut down cleanly; pick an image,
restore it, and go. If they don't, pick the highest count and restore
that, possibly with dire warnings about how your data may have been
thoroughly mangled.

The 1U thing sounds a little on the large size, but for cost I suppose
it may be the easiest bang for the buck. A quick, pretty mindless
check of Dell suggests that for just over $2300 you could get a system
with a adequate CPU, 3GB of RAM, and two 40GB disks.

Note that writing 2GB to disk takes time, and writing it twice takes
longer. And UPSs die.

-Jim

Malc.

You can grab our iSCSI target/initiator software (StarWind/StarPort).
It has a feature of creating iSCSI mapped RAM disk. As our stuff is
free for non-commercial use at least you'll be able to experiment and
know for sure would such a solution work for you or not ))

Regards,
Anton Kolomyeytsev

CEO, Rocket Division Software

Malcolm Weir wrote in message . ..
On 29 Nov 2004 09:35:52 -0800, (Jim Wall) wrote:

I am looking to find a low cost SCSI storage unit that is both very
fast, and has permanent store capabilities. I am envisioning a 1U box
that essentially is one big RAMDISK. And it has a battery and a hard
drive, so in the event of a power failure, all the data in the RAM
disk can be flushed to the hard drive. A gigabyte or two is all the
storage that I need for the RAMDISK. I have found Imperial Technology,
but their prices are way out of the range I am interested in.

Your problem will be the software. Sure, creating a (say) 2GB
ram-based storage thing that dumps to an HDD when a UPS says "No AC"
is not hard, but making that thing look like a parallel or FC SCSI
target is harder. Although making it look like an iSCSI target may be
a "solved problem".

I, being paranoid (and experienced) would go with two HDDs, not just
one, and use a system that periodically writes the RAM to alternating
HDDs, then updates a "generation" count on the disk. On shutdown, you
just have to copy the current image to the next disk to be safe, and
then copies it to other disk to be safer. Bootup becomes relatively
easy: if the generations match, you shut down cleanly; pick an image,
restore it, and go. If they don't, pick the highest count and restore
that, possibly with dire warnings about how your data may have been
thoroughly mangled.

The 1U thing sounds a little on the large size, but for cost I suppose
it may be the easiest bang for the buck. A quick, pretty mindless
check of Dell suggests that for just over $2300 you could get a system
with a adequate CPU, 3GB of RAM, and two 40GB disks.

Note that writing 2GB to disk takes time, and writing it twice takes
longer. And UPSs die.

-Jim

Malc.

Maybe I don't understand the problem.

But why not buy a RAID controller with expandeble cache ram and a battery
option ???
I've even seen lowend RAID controllers which you could expand with standard
RAM modules
up to at least 512mb ?

With your requiments (1-2Gb of disk) you cannot have very much sustained
writes..
So I would go for lots of main memory used for diskcache (on OS-level) and
the write cache of
the controller for fast writes.


regards,
Carsten


"Anton Kolomyeytsev" skrev i en meddelelse
om...
You can grab our iSCSI target/initiator software (StarWind/StarPort).
It has a feature of creating iSCSI mapped RAM disk. As our stuff is
free for non-commercial use at least you'll be able to experiment and
know for sure would such a solution work for you or not ))

Regards,
Anton Kolomyeytsev

CEO, Rocket Division Software

Malcolm Weir wrote in message
. ..
On 29 Nov 2004 09:35:52 -0800, (Jim Wall) wrote:

I am looking to find a low cost SCSI storage unit that is both very
fast, and has permanent store capabilities. I am envisioning a 1U box
that essentially is one big RAMDISK. And it has a battery and a hard
drive, so in the event of a power failure, all the data in the RAM
disk can be flushed to the hard drive. A gigabyte or two is all the
storage that I need for the RAMDISK. I have found Imperial Technology,
but their prices are way out of the range I am interested in.

Your problem will be the software. Sure, creating a (say) 2GB
ram-based storage thing that dumps to an HDD when a UPS says "No AC"
is not hard, but making that thing look like a parallel or FC SCSI
target is harder. Although making it look like an iSCSI target may be
a "solved problem".

I, being paranoid (and experienced) would go with two HDDs, not just
one, and use a system that periodically writes the RAM to alternating
HDDs, then updates a "generation" count on the disk. On shutdown, you
just have to copy the current image to the next disk to be safe, and
then copies it to other disk to be safer. Bootup becomes relatively
easy: if the generations match, you shut down cleanly; pick an image,
restore it, and go. If they don't, pick the highest count and restore
that, possibly with dire warnings about how your data may have been
thoroughly mangled.

The 1U thing sounds a little on the large size, but for cost I suppose
it may be the easiest bang for the buck. A quick, pretty mindless
check of Dell suggests that for just over $2300 you could get a system
with a adequate CPU, 3GB of RAM, and two 40GB disks.

Note that writing 2GB to disk takes time, and writing it twice takes
longer. And UPSs die.

-Jim

Malc.