Is It Possible To Raid0 Sd Cards With Pandora?


ferg

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and would the I2C controller show any bandwidth improvements? Is there anyway we can add a third SD slot? Any developers attempted to do this?
 
It is probably possible with software RAID, but if I've understood correctly there's little advantage (certainly of RAID 0) as the data bus isn't much faster than a single decent speed SD card.

Also people keep asking about I²C, but it is a relatively slow interface, only 3.4Mbit at high speed:
http://en.wikipedia.org/wiki/I%C2%B2C
 
Sugestion: Use 2 SDs of the same size in each slot and use them at RAID1 !!! =D

Serioulsy, I don't see the point in raid0 for Panda. If you want extra speed/performance, you should just go for a higher class SD.
 
pelrun said:
*twitch* :blink:

Geez, you get two slots and you're asking for THREE? Use a usb adapter if you're that desperate for silly hardware configurations.

3 SD cards would put it them in 60 ~ 90MB if the scaling was linear add to that SD card's lower access time and you get around 100GB of storage plus HDD speed on a little ARM portable box.
 
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Near-kun said:
Sugestion: Use 2 SDs of the same size in each slot and use them at RAID1 !!! =D

Serioulsy, I don't see the point in raid0 for Panda. If you want extra speed/performance, you should just go for a higher class SD.

That wouldn't net much performance, especially with each slot having a bandwidth cap.
 
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ferg said:
3 SD cards would put it them in 60 ~ 90MB if the scaling was linear add to that SD card's lower access time and you get around 100GB of storage plus HDD speed on a little ARM portable box.
If you don't raid them, you can just swap them out as you need, giving you limitless storage.
You won't see the kind of speed boost you seem to be expecting by configuring a raid.
 
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ferg said:
That wouldn't net much performance, especially with each slot having a bandwidth cap.
Each slot doesn't have a bandwidth cap, the whole thing has a bandwidth cap.
 
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WizardStan said:
ferg said:
That wouldn't net much performance, especially with each slot having a bandwidth cap.
Each slot doesn't have a bandwidth cap, the whole thing has a bandwidth cap.

That's what I thought o.o
 
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Aren't the slot fed by a single-channel SD controller? So you read/write one slot at the time in any case. My N800 works that way, so trying to double the speed by striping the two slots won't give any speed increase.
 
I'm about to shoot off, but this should cover some questions that may crop up regarding this again (hopefully linking correct page)
Raid0 discussion
 
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Again - lots of speculation and declaration by people who don't have one of the final boards. As far as I can tell the 'cap' has never been firmly established from a hardware spec perspective OR from real world testing.

Whether or not any speed gain could be garnered by RAID0 SDHC cards - and if there is a cap - is yet to be seen.

It may even be possible to build a hardware RAID0 out of it - but it would likely require a special driver to be written and updated to the OS that resides in flash. In -theory- a person could build the cards as a RAID 0 and then place a boot loader in place of the Flashed OS - but thats a lot of moving parts to figure out.

There may be a bus-hardware limitation cap. We don't know, or at least no-one has posted, what this cap really is. If there is a hardware cap on the device, then real-world testing is still appropriate. The real world performance will likely be something less than the cap and may vary over different cards.

The hardware may actually be able to keep up with the fastest cards - making the card itself the cap.

Until someone with a production board OR a real Pandora console has the time, money (for the cards), skill set and inclination to do some real world testing - this item will be unanswerable. Everything else I have seen on this topic is from people pulling stuff out of their Miscellaneous Information Access Sub-System or parroting and linking to stuff they have seen others make up on the fly before.

So, who's got the time, money, skill set and inclination AND either a final board OR an actual Pandora? It might be some time before we can really answer this.

IMHO.
 
Actually, MWeston posted quite a while ago that the bus was limited to 24 MB/s, that was shared between the two slots, and so RAID 0 wouldn't enable any significant performance gains. Unfortunately, I can't find the post, because for some reason MWeston's post history apparently only includes either a certain number of posts, or only posts back to a certain time. Google was similarly unhelpful - maybe problems caused by the board upgrade.
 
FWIW, that's a post I remember reading myself.
 
Tom` said:
Unfortunately, I can't find the post, because for some reason MWeston's post history apparently only includes either a certain number of posts, or only posts back to a certain time. Google was similarly unhelpful - maybe problems caused by the board upgrade.
To avoid the cutoff, you have to do an advanced search and specify a date range. I just set it to between 2003 and now.

MWeston said:
24MB/s based on a 48MHz clock, 4 bit SDIO
 
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Chip said:
Tom` said:
Unfortunately, I can't find the post, because for some reason MWeston's post history apparently only includes either a certain number of posts, or only posts back to a certain time. Google was similarly unhelpful - maybe problems caused by the board upgrade.
To avoid the cutoff, you have to do an advanced search and specify a date range. I just set it to between 2003 and now.

MWeston said:
24MB/s based on a 48MHz clock, 4 bit SDIO
Thank you! Finally - a real data point. VERY good find.

Looking at SDHC card benchmarks on:
Tom's SDHC benchmarks
It looks like:
Class 4 card average read speeds top out around 15MB/sec
Class 6 card average read speeds top out around 19.6MB/sec
So, in theory, the limiting factor with these would be the cards themselves.

There is no 3rd party benchmarking data yet that I can find for the new class 10 cards. However, SanDisk is claiming 30MB/sec reads/writes:
SanDisk 32GB SDHC class 10 card
We would not likely be able to top out that card and it would be limited to the board throughput. Still - this MAY be 20+% faster 24MB/sec bus with 30MB/sec card = <24MB/sec VS using a 19.6MB/sec card.

All of this winds up being theoretical though since nobody has tested a high end class 6 card, let alone the new class 10 cards in a Pandora.

We do know, now, that there is a cap. However, the claims that the cap would limit the card to Class 2 or Class 4 performance strikes me as bunk. That would be 10-15MB/sec not 24MB/sec. In theory the class 6 cards would be appropriate and about 30% faster than the class 4. Whether or not any speed gains could be seen from using a class 10 card... it all depends on how much of the 24MB/sec bus we can actually use. If we can get the whole thing, then a class 10 card potentially being 20% faster than a class 6 -might- make sense to some people.

This -does- shoot down the RAID0 for performance thing, unless you're using class 4 or slower cards to begin with.

We didn't all buy our Pandora with our lunch money. I would like to purchase a set of cards that top out the performance of the handheld - if the gain going from a class 4 to class 6 or class 10 is negligible, I'll save my money for the Pandorappstore.

Anxiously awaiting benchmarks - but we're going to need some standardized way to do it.
 
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Also that bus speed is theoretical. Expect a good Class 6 to be as high as you need to go. PCI's 32-bit bus can theoretically go 133MB/s, But I was only able to push around 100.

I would expect the *actual* throughput to be around 18-19 MB/s
 
A little research later...

It looks like Patriot memory has a $105 Class 10 card now on NewEgg. May not be as fast as the Sandisk - but there isn't comparative benchmarks on any of this... all speculation. But regardless, Class 10 prices are not what they were. Once I know my Pandora is on it's way, I'll likely buy one of these just to see if it gets different performance from my 32GB Kingston class 4 card. It should...

It looks like Toshiba is going to have a 32GB SDHC card coming out early spring with 60MB/sec reads and 30MB/sec writes. Way overboard for our device BUT I like the direction things are going. That one would max out the DTR on writes too.

What is a good Linux media benchmark program that we can get on both ARM and X86?
 
You probably wouldn't see any performance boost off of software RAID (which is essentially what you'd be doing - but software RAID usually needs an onboard RAID micro-controller) given the hardware. If anything, RAID1 (mirroring) - but still - no. Just, no.

You may want to consider running a SPAN via LVM across the SD cards (even that may depend on the device/OS, but it *is* running Linux so it's possible - moreso than RAID).

==Edit 2==

Also, as far as adding additional storage, that USB port is dual purpose :) You could add additional storage if you wanted to... I was actually just pondering the possibility of using a physical hard disk on a hub (out of sheer curiosity, one wonders if a SWAP partition would do anything) for when I don't have it on the road.

That's the thing with having what is essentially a portable gaming computer :D

Nothing saying it can't be done (as long as there is support for said "thing").
 
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