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How to use a terabyte of RAM

How to use a terabyte of RAM

Posted Mar 13, 2008 3:20 UTC (Thu) by dlang (subscriber, #313)
Parent article: How to use a terabyte of RAM

the Violin box appears to the system like any other external SCSI device. it implements it's
own battery and backup mechinism, so ramback is not relavent to it.


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How to use a terabyte of RAM

Posted Mar 13, 2008 4:28 UTC (Thu) by zlynx (subscriber, #2285) [Link]

It would be relevant if the Violin was running Linux as its embedded OS.

How to use a terabyte of RAM

Posted Mar 13, 2008 5:37 UTC (Thu) by daniel (guest, #3181) [Link]

"It would be relevant if the Violin was running Linux as its embedded OS."

It is.

How to use a terabyte of RAM

Posted Mar 14, 2008 21:47 UTC (Fri) by dlang (subscriber, #313) [Link]

but the storage does not show up as system memory, even inside violin

since it can be either 500G of ram or a much larger amount of flash, I'm sure that it shows up
to the Linux OS on the system as storage of some sort, not as system Ram

How to use a terabyte of RAM

Posted Mar 15, 2008 0:05 UTC (Sat) by nix (subscriber, #2304) [Link]

Until recently I'd have suspected that the page replacement algorithms 
would scream and die at the sight of that much RAM, but I've seen logs of 
systems with 1.5Tb of accessible RAM, so this sort of thing is happening. 
(That was a big Altix, IIRC.)

How to use a terabyte of RAM

Posted Mar 13, 2008 5:37 UTC (Thu) by daniel (guest, #3181) [Link]

"the Violin box appears to the system like any other external SCSI device. it implements it's
own battery and backup mechinism, so ramback is not relavent to it."

The violin box does not appear as a scsi device, but as a _much_ faster PCI-e (external)
device.  For which Violin has written a driver to make it appear as a block device.  They also
have a driver to make it appear as memory, but I have not tried that.

The Violin plays only for a single one-ear box, or for small groups with two ears as well?

Posted Mar 13, 2008 17:05 UTC (Thu) by hmh (subscriber, #3838) [Link]

Just curious: How many PCIe ports a violin box has?  Can I have redundant connections (two
PCIe HBAs per host)?  Can I plug various hosts to the violin, much like I could with a storage
with multiple FC ports?

This sort of information really should be in their webpages, but I have failed to locate it
anywhere.

The Violin plays only for a single one-ear box, or for small groups with two ears as well?

Posted Mar 15, 2008 19:24 UTC (Sat) by daniel (guest, #3181) [Link]

The Violin 1010 box has two PCI-e 8x (external) links, each delivering about 1.7 Gbytes/sec of
read throughput that can be connected in parallel to the same host for over 3 GB/sec of read
bandwidth, or connected to two different hosts for redudancy.

They really out to post this info in a blinking, scrolling banner on their site, if ask me.

The Violin plays only for a single one-ear box, or for small groups with two ears as well?

Posted Mar 15, 2008 23:37 UTC (Sat) by hmh (subscriber, #3838) [Link]

Agreed.  Nobody sane would bother to buy a US$50k+ storage unit without knowing this
information first, it is weird to not publish it up front.

Two ports is way too little for this class of hardware, IMO.  They need to add two more.

One needs two ports per host for HBI and cabling redundancy, and usually one will also need to
be able to connect a minimum of two separate hosts to the same storage (for HA redundancy).
Typically, a high-uptime HA setup would have two hosts connected via two PCIe links each to two
Violin boxes.

also as ram

Posted Mar 14, 2008 3:33 UTC (Fri) by ccyoung (guest, #16340) [Link]

sell ram itself if DDR2 packaging, so this becomes immediately feasible.

http://www.violin-memory.com/products/vimms.html

and, with next gen flash gets rid of power objections.

also as ram

Posted Mar 15, 2008 19:28 UTC (Sat) by daniel (guest, #3181) [Link]

"next gen flash gets rid of power objections"

It does and it doesn't.  A box with a heavy continuous write load will eventually end up with
all its "buffer" flash in erase mode, and write throughput will drop down to erase speed.  So
RAM will always be better than flash for high performance transactional setups, but less
demanding loads will be fine with flash.

How to use a terabyte of RAM

Posted Mar 14, 2008 20:03 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

I'm getting confused. What is the relationship between Ramback and Violin?

How to use a terabyte of RAM

Posted Mar 14, 2008 21:48 UTC (Fri) by dlang (subscriber, #313) [Link]

the existance of the violin is being used as evidence that something liek Ramback is needed

How to use a terabyte of RAM

Posted Mar 14, 2008 22:07 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

Thanks. Much clearer now.

If I have 500 GB of memory, Violin looks like a much better way than Ramback to use it. The reason is that it better answers my mistrust of the battery, hardware, and Linux. I can put multiple Violins in a RAID array and when the battery, hardware, or Linux fails in one, I don't lose data. And it looks roughly as fast as Ramback.

If I do put 500 GB of memory in the application server, I think I'd just like to add it to the pool and let the memory manager decide if caching all the contents of my filesystems is the best use for it. Maybe with some parameters to say I trust my battery, hardware, and Linux enough that Linux need not hurry to write any of it back to disk.

How to use a terabyte of RAM

Posted Mar 15, 2008 19:32 UTC (Sat) by daniel (guest, #3181) [Link]

"Violin looks like a much better way than Ramback to use it. The reason is that it better
answers my mistrust of the battery, hardware, and Linux. I can put multiple Violins in a RAID
array and when the battery, hardware, or Linux fails in one, I don't lose data. And it looks
roughly as fast as Ramback."

It is exactly as fast as ramback, because it is ramback.  Ramback was written to provide the
Violin box with stable backing store.  It is just a nice bonus that ramback happens to be
useful for ramdisks in general, and for my code hacking workstation in particular.

How to use a terabyte of RAM

Posted Mar 15, 2008 22:30 UTC (Sat) by giraffedata (subscriber, #1954) [Link]

OK, then, based on that and some more reading, I believe the answer to my question, "what is the relationship between Ramback and Violin" is this: Ramback couples a nonpersistent block device (a device that doesn't retain its memory across an orderly shutdown) with persistent storage so as to create a block device with the speed of RAM and the persistence of disk. The violin box is one source of a nonpersistent block device, and the one that inspired Ramback. The box uses DRAM for storage and connects to the application server via PCI express and comes with a driver for Linux to make a Linux block device out of it. Ramback, running on the application server, uses that block device.

That means my earlier comments comparing use of Violin with use of Ramback are nonsense; they aren't alternatives because one provides persistent storage and the other doesn't. And my comparison of using Ramback to adding memory to the regular pool is similarly nonsense because Ramback can use DRAM that isn't in the application server (e.g. the Violin box).


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