SD cards performance and testing

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jcb:
This subject was raised in the Tascam DR-70D discussion due to the perceived "pickiness" of this recorder regarding SD cards. It was time to start a dedicated thread to discuss what kind of performance we expect from memory cards and how to check that we get what we need.

For reference, the Tascam DR-70D thread hijack began around here : http://taperssection.com/index.php?topic=174900.msg2163449#msg2163449 and it was my fault.

So what do we know ?

* Most recorders come wit a list of approved/tested media. When using non-recommended cards, problems will be blamed on the card.
* A number of fake or dubious cards are being sold through different channels (ebay, ...)
* Recording one channel at 24/96 with 20% overhead requires writing 24 x 96 / 8 = 345 kB/s to the card.
* So 4 channels require roughly 1.5MB/s bandwith when writing to the card.
* Some recent class 10/UHS-I cards seem to have very good write performance (more than 60 MB/s) whether they have to write sequential or random data and they never slow down temporarily.
* Other recent class 10/UHS-I cards will dislay a decent average write rate for sequential data (35MB/s) that is more than needed but slow down considerably when writing random data (8MB/s) with at times a very limited bandwidth (less than 1MB/s) which may be a real problem.
What can we test (please excuse my ignorance : I don't do windows and never used a mac so I do not know many useful tools) ?

* Fake cards can be identified with H2testw on windows or f3 http://oss.digirati.com.br/f3/ on linux.
* f3 has an uility (f3write) that tests the average write speed of the card for 1GB files. Something similar may exist on windows.
* gnome_disks_utility ("disks" in the gnome menu) allows for random write testing on linux. Something similar probably exists for windows.
What can we (yet) not test ?

* A recorder writes 1 to many (depending on the number of channels) files at the same time. What are the cards performance in this case ? How might we test this ?

aaronji:
I think fio will do what you need it to do (generating an arbitrary number of sequential files, like audio recording) and benchmark the card's performance.

I think your 20% overhead is probably highly conservative; where does that number come from?

kleiner Rainer:
Did some tests with CrystalDiskMark Portable today:

Lexar 64GB, Class 10 SDXC:

-----------------------------------------------------------------------
CrystalDiskMark 5.0.3 (C) 2007-2015 hiyohiyo
Crystal Dew World : http://crystalmark.info/
-----------------------------------------------------------------------
* MB/s = 1,000,000 bytes/s [SATA/600 = 600,000,000 bytes/s]
* KB = 1000 bytes, KiB = 1024 bytes

Sequential Read (Q= 32,T= 1) : 17.565 MB/s
Sequential Write (Q= 32,T= 1) : 15.519 MB/s
Random Read 4KiB (Q= 32,T= 1) : 3.259 MB/s [ 795.7 IOPS]
Random Write 4KiB (Q= 32,T= 1) : 0.005 MB/s [ 1.2 IOPS] :o
Sequential Read (T= 1) : 17.198 MB/s
Sequential Write (T= 1) : 15.309 MB/s
Random Read 4KiB (Q= 1,T= 1) : 2.987 MB/s [ 729.2 IOPS]
Random Write 4KiB (Q= 1,T= 1) : 0.005 MB/s [ 1.2 IOPS] :o

Test : 1024 MiB [I: 8.4% (5.0/59.6 GiB)] (x5) [Interval=5 sec]
Date : 2015/11/15 11:32:31
OS : Windows 7 Starter SP1 [6.1 Build 7601] (x86)

Sandisk Ultra 32GB, Class 10 micro SD:

-----------------------------------------------------------------------
CrystalDiskMark 5.0.3 (C) 2007-2015 hiyohiyo
Crystal Dew World : http://crystalmark.info/
-----------------------------------------------------------------------
* MB/s = 1,000,000 bytes/s [SATA/600 = 600,000,000 bytes/s]
* KB = 1000 bytes, KiB = 1024 bytes

Sequential Read (Q= 32,T= 1) : 18.742 MB/s
Sequential Write (Q= 32,T= 1) : 17.801 MB/s
Random Read 4KiB (Q= 32,T= 1) : 3.394 MB/s [ 828.6 IOPS]
Random Write 4KiB (Q= 32,T= 1) : 1.969 MB/s [ 480.7 IOPS]
Sequential Read (T= 1) : 18.457 MB/s
Sequential Write (T= 1) : 17.617 MB/s
Random Read 4KiB (Q= 1,T= 1) : 3.148 MB/s [ 768.6 IOPS]
Random Write 4KiB (Q= 1,T= 1) : 1.841 MB/s [ 449.5 IOPS]

Test : 1024 MiB [I: 0.0% (0.0/28.8 GiB)] (x5) [Interval=5 sec]
Date : 2015/11/18 22:30:42
OS : Windows 7 Starter SP1 [6.1 Build 7601] (x86)

Seems like the "Random Write" performance is the limiting factor in uses other than sequential writing of a video/audio stream.

Greetings,

Rainer

voltronic:
^ Wow! I second your use of emoji there! I'm assuming a fresh full format on each card before testing?

Thanks for linking this tool and your results - this looks better than some others out there.

aaronji:

--- Quote from: kleiner Rainer on November 18, 2015, 06:42:46 PM ---Seems like the "Random Write" performance is the limiting factor in uses other than sequential writing of a video/audio stream.

--- End quote ---

You can find some white papers describing this if you poke around on the web a bit...

Nice to see that the cards you tested were way above their speed class.

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