Does anyone yet make a TB Flash memory in a 3.5" drive physical format. If
so, could you pass on a reference? The interface would need to support
about at a 400MB/s sustained rate. I can work with any interface such as
Fiber Channel or whatever .
thanks for any tips

trs80 <trs80 (AT) yahoo (DOT) com> wrote:
Nobody does and nobody gets that rate, not even for large
accesses. Although some manufacturers have SATA3 drives
planned with internal excessive multi channel architectures.
For small accesses FLASH can be significantly slower than
disks.

For what you want, you may want to look at a traditional RAM
fronted disk. Will be expensive though and definitely
not available in 3.5". Alternatively you could build a
RAID0 with a really fast controller and FLASH disks.

Arno

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Barry OGrady wrote:
Flash drives are not normally considered "slow" - read performance of
200+ MB/s, and writes of maybe 70 MB/s are possible with good drives.
That's a lot faster for reading than even top-range hard disks, and
similar for writing (the OP doesn't specify if they want reading or
writing speeds).

I agree about the sizes - you don't get flash drives as big as 1 TB at
the moment (at least, not in standard 3.5" formats).


As for write endurance, you are about a decade out of touch...

<http://www.storagesearch.com/ssdmyths-endurance.html>

Arno wrote:
There are a number of very fast drives available, but the cost is
significant - a raid would be much more cost-effective. The biggest
single drive I found in a quick check was:

<http://www.plianttechnology.com/lightning_ls.php>

That's 300 GB in 3.5" SAS, rated at 525/340 MB/s.

Of course, for the fastest devices you use a PCI Express card with RAM
rather than flash...

David Brown <david.brown (AT) hesbynett (DOT) removethisbit.no> wrote:
Indeed. however a RAID0 with relatively cheap disks will give you
200+MB/s read and write speeds for large accesses. A 4-way
RAID0 (possible at least with Linux software RAID and likely with
the xBSDs as well) should reach 400MB/s large access speed.

For small accesses the story is different, onlt a RAM frontend will
reach this speed here, FLASH may be even slower than disk here,
especially on write.


Well, not for USB flash. I did recently torture a 2GB Kingston
USB to death and it had consistent data errors (with no error
meassege to make matter worse!) after about 3500 full overwrites.

Say the OP wants to overwrite his disk at 400MB/s, then 3500
full operwrites are reached after about 100 days of operation.

I expect SATA FLASH is better, but not all may be. What however
does not happen with modern FLASH is that writing a few 1000
times to a single location kills the drive. Traditional FLASH
without wear leveling had that problem, with some dying
after 10000...100000 writes to the same sector.

Arno
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Arno wrote:
I agree that raid is the cost-efficient way to get this sort of
bandwidth (the cost-inefficient way being a PCI slot ram disk).

Small read accesses are extremely fast with flash disks - far faster
than with hard disks, since small reads are dominated by the seek times.

For small writes, it is certainly true that these are slower to complete
on a flash disk than on a hard disk, and less efficient than streamed
writes. But outside of synthetic benchmarks, so what? Small writes are
cached by the OS - as far as the application is concerned, they happen
almost instantaneously. And as long as you don't have too many of them
flushing to the disk at the same time, the writes are not going to cause
other performance issues for the flash disk - if the disk needs to read
from the same flash chip, the erase/write can be paused temporarily.
You'll only see a real-world problem if you are dealing with an
application that makes small writes and lots of fsyncs, combined with an
older flash drive that is poor at hiding the garbage collection.

USB flash devices are generally optimised for low costs rather than high
quality or high endurance. They also often have very poor erase block
management, since they have few chips and also must minimise the risk of
data loss if the device is removed unexpectedly. This means a single
block write to the device can cause many erase/writes to the flash.

He doesn't say whether he wants to stream reads or writes, or how long
he wants to sustain the transfers. My guess would be that he'd like to
break off writing and do the occasional read - there are not many
applications which produce new data at a rate of 34 TB per day, nothing
of which needs to be kept for more than forty minutes!

Modern SLC flash chips will have endurance in the range of at least a
million erase/writes if you are nice to them (i.e., keep them at room
temperature). MLC devices used in cheaper disks have significantly
lower endurance.

So for continuous writing using good SLC disks, he's got an average of
something like 80 years before write endurance is a problem.

great inputs. thanks for the help
"trs80" <trs80 (AT) YAHOO (DOT) COM> wrote

David Brown <david.brown (AT) hesbynett (DOT) removethisbit.no> wrote:
True.

I can think of an application or two that needs this. Quite
specialized though.

So here is a question to the OP: What is your access profile?

Yes, but even cheaper MLCs should be at 100'000 cycles today, that
is why I find the 3500 overwrites figure I found so disappointing,
and this thing uses an Intel flash memory chip, not some unpranded
or Tier-3 vendor product.

Expensive SLC is very hard to break and should indeed survive
decades at full write rate.

Arno
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Arno <me (AT) privacy (DOT) net> kenjka:
MLC's often have at max 10.000 E/W cycles... SLC's have around 100.000...
Reference is EMC's and STEC documentation for EFD drives (in fact it's STEC
ZeusIOPS)...

My calculations say that 400GB SLC drive can last 150 years with 24/7/365
writes on it (SLC, 100.000 E/W cycles)...

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calypso (AT) fly (DOT) srk.fer.hr.invalid wrote:

Ok, say 400GB at 200MB/s. That gives 1.8 overwrites/h, i.e. about
55'000h, i.e. about 6.25 years. Sorry your math is off. And
the 6.25 years are with perfect wear leveling. Assuming my
experience of death after 3'500 cycles with 10'000 cycle MLC,
the disk could die as early as within 2 years.

Even 1'000'000 cycle MLC only gives you 20-60 years.

Arno
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