Class Number for SD cards

What class numbers should one look for when buying an SD card for Raspberry-Pi, for Beagleboard and for Pandaboard?
What is the class number of the RISC OS Pi card?

I think transfer speeds can vary within a particular class (number). In which case, what transfer speeds should one consider for each of the three machines?

My advise would be go for class 10…
Then go for as fast as possible…
I Use SanDisk Extreme which is labeled as 45MB/s
That’s on my Pandaboard ES.
I had some strangeness on my pi though.
On my early Pi the Sandisk Extreme worked fine, but it wouldn’t work on the 512MB model…
There is a list of recommended SD Cards for the Pi
http://elinux.org/RPi_SD_cards

It really shouldn’t matter for a Beagleboard as it’s only used at start up. Once it’s running you can even remove the SD. I use class 4 as they’re cheap enough to consider disposable.

The one card system is also possible with the Beagle xM. I have a card with two partitons that works. But it works not with all cards.

I have read that some of the fastest class 10 SD cards have a very poor performance when reading and writing to lots of small random access files. These cards are generally optimised to give good benchmark results for large file read and writes – e.g. saving piccies on digital cameras etc. So you might get better average performance using a cheap class 4 or class 6 card on RISC OS, rather then with a 32X class 10 card or whatever. YMMV.

Ralph

I have a Samsung 32GB class 6 microSD card (this one though it was cheaper and in stock a month ago). Haven’t tried it on a Pi, but I’m using it as an SSD on my netbook and it’s about as quick as the internal SSD. It was specifically chosen over a class 10 to have a good random write performance (the user-contributed Amazon picture says 2MB/s for random 4KB writes which sounds about right – some class 10 cards get 0.01MB/s).

Amazon is a good place to buy if you’re looking for speed measurements, because of the user-contributed pictures of speed test results on some cards. Apparently the SanDisk microSD 32GBs have a high failure rate, which is why I went for a Samsung.

Browsing the Odroid website I came across this:

eMMC Module (64GB) THGBM5G9B8JBAIE 64Gbyte eMMC Version 4.41 interface with 19nm NAND from Toshiba. 50Mhz 8bit DDR fast interface. It is about 200% faster than SD Card Class 10

http://www.hardkernel.com/renewal_2011/products/prdt_info.php

Shame we don’t have a eMMC socket :-(
Tasty looking board too btw

I have read that some of the fastest class 10 SD cards have a very poor performance when reading and writing to lots of small random access files.

I have got a 8Gbyte Sandisk class 10 Extreme Pro (quoted as 95Mbytes/s) [cost £19.99 at PC World] for my Pandaboard ES and it is extremely fast when copying the whole disc image from a network drive. I can see ‘Reading’ for some time as each file or each megabyte of a large file is read in over the network and then ‘Writing’ appears and disappears so quickly as not to be seen at all.

However although it is an 8Gbyte card, the filecore disc size is 2Gbytes – perhaps this avoids some of the difficulties with larger disc sizes requiring larger allocation units.

The benchmarks give about 15Mbytes/s for writing and 21 Mbytes/s for reading (the benchmarks are based on reading and writing a 1Mbyte file but I suspect larger files are even quicker). Repeating the benchmarks with 4k files rather than 1M files and the read speed drops to 6Mbyte/s and the write speed to 1Mbyte/s. With 8M files, it increases to 22Mb/s (read) and 17Mb/s (write).

I have added a 6Gbyte FAT partition above the filecore and FAT partitions (i.e. in the otherwise unused bit of the card, using Ubuntu v10 on my PC) but haven’t yet found a way for RISC OS/DOSFS/Fat32fs to see and use it. Any ideas please?

Another unbranded class 10 8G byte card (from Maplin) is woefully slow.

I have added a 6Gbyte FAT partition above the filecore and FAT partitions (i.e. in the otherwise unused bit of the card, using Ubuntu v10 on my PC) but haven’t yet found a way for RISC OS/DOSFS/Fat32fs to see and use it. Any ideas please?

I have an obey file with:

IfThere <Obey$Dir>.Fat32Fs Then Rmensure Fat32Fs 1.42 RmLoad <Obey$Dir>.Fat32Fs
fat32fs:mount -fp2 :16 { > null: }
addtinydir fat32fs::16

addtinydir fat32fs::16

This does not open the 6G partition and gives me the error ‘Could not open filesystem’

try ‘addtinydir Fat32fs::fat32_16.$’ – works fine for me. Not sure of the size limitations for a Fat32 file system – for what it’s worth, I have a 4GB card with 2GB for Fat32

same result. Should ’fat32fs:mount -fp2 :16 produce any output? It does not for me.

“fat32fs:mount -fp2 :16” should

• print “Mounting drive 16 partition 2”
• launch a filer window from the second partition of SDFS drive 0.
• if it prints “Could not open drive 16 (-20).”, you are trying to open a non-existing partition.

What does “fat32fs:fatinfo” give, after you have tried to mount?
Which version has your fat32fs module?
What is in your partition table? use Ubuntu

Ah! Silly me. Many thanks for the help. I have updated the version to 1.42 (was 1.39) and altered the !Run file in !Boot.Choices.Boot.PreDesk.Fat32fs to say

IfThere <Obey$Dir>.Fat32Fs Then Rmensure Fat32Fs 1.42 RmLoad <Obey$Dir>.Fat32Fs
fat32fs:mount -fp2 :16 { > null: }
addtinydir fat32fs::16

and I now get a folder called ‘$’ on the icon bar which when clicked upon opens a filer window ‘Fat32fs::RISC OS.$’ which is the unused part of the SD card above the FAT and filecore partitions. So I have access to the small FAT partition via SDFS::0.$.!Boot.Loader. Also as I have a 8Gbyte SD card, this gives me a filecore partition of 1880Mbytes plus the remainder of the card (6Gbytes) under Fat32fs. The fat32fs partition now has a much faster read/write speed than the SDFS for small files – 10Mbytes/s (read) 7 Mbytes/s (write) for 4k files and the same 21Mbytes/s (read) and 17Mbytes/s (write) for 1M files (8M files are the same as for SDFS).

Is there any way to get a drive icon for this drive on the icon bar please?

*fat32fs:fatinfo
Drive 16 is connected (FAT32)
Volume name         = RISC OS
Drive size          = 5688 Mbytes
Free space          = 5677 Mbytes
Total sectors       = 11650730
Total clusters      = 1453497
Free clusters       = 1453495
Next Free cluster   = 4
Bytes per sector    = 512
Log2 Bytes per sctr = 9
Sectors per cluster = 8
Reserved sectors    = 32
Number of FATS      = 2
Root Entry count    = 0
Root cluster        = 2
Qty of Buffers      = 256/2048
File sectorcount          = 15508990
File SectorsPerCluster    = 8
File ClusterReadAheadSize = 6
File MaxSectorsPerRead    = 1024
File MaxSectorsPerWrite   = 1024
Open files:
Drive = 16
Fileswitch handle = 251

I’ve now rebooted the machine and using the same !Run file I am just getting the PiBoot partition (which is no use of course). Puzzled.

Answered my own question.

Altered the !Run file in !Boot.Choices.Boot.PreDesk. to

IfThere <Obey$Dir>.Fat32Fs Then Rmensure Fat32Fs 1.42 RmLoad <Obey$Dir>.Fat32Fs

and added a file OpenFAT to !Boot.Choices.Boot.Tasks.

fat32fs:dismount :16 { > null: }
fat32fs:mount -fp2 :16 { > null: }
addtinydir fat32fs::16

The dismount is needed as fat32fs mounts the PiBoot partition (by default, in PreDesk as the module loads) and any further partition information is ignored if a drive is already mounted.

Now I get a 6Gbyte fat32fs partition as Fat32fs::Panda.$
plus an 1880 Mbyte filecore partition as SDFS::RISCOS.$
plus the 128Mbyte FAT partition as SDFS::RISCOS.$.!Boot.Loader
all visible at the same time on the same SD card.

The complication is worth it as fat32fs is faster than SDFS. And you need SDFS as you can’t boot from fat32fs.

Would be nice to have a proper drive icon rather than a directory symbol on the icon bar. Also to have a ‘free’ utility etc. as for a normal drive icon.

The complication is worth it as fat32fs is faster than SDFS. And you need SDFS as you can’t boot from fat32fs.

Old thread, I know, but does this still hold true for newer SDFS and FAT32 stuff?