Nick Keighley
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SDs and micro SDs

Sat Jan 03, 2015 2:20 pm

Hi,

I bought a starter kit (Iridium Starter Kit from The Pi Shop) hoping to avoid those annoying trips down to the shop to get yet another essential bit/cable etc.).

Fair enough it needs batteries (nice if they'd mentioned that though). The kit includes a Raspberry SD card presumably with pre-loaded software, and a model B+ Raspberry Pi. The model B+ uses micro-SDs, so what are my options? Are there micro-SD/SD adaptors? Can I copy the software from SD to micro-SD? I assume I need a fairly large micro-SD- 512M?

jamesh
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Re: SDs and micro SDs

Sat Jan 03, 2015 3:44 pm

Most uSD cards come with SD adapters. They are passive devices, since uSD and SD are effectively the same things in different packages. Have you checked the SD card that came with you kit to see if its a adapter with uSD in it already? That's usually the case.

I think a 8GB card is a sensible size vs price compromise.
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Re: SDs and micro SDs

Sat Jan 03, 2015 3:50 pm

8 gig micro sd cards can be pretty cheap, I bought several at just over £4 each last month. Class 4 or class 6 cards are better for use with a pi than class 10 cards.

I've had two noobs cards (Raspberry logo on front), they were both SD adaptors with a micro SD card inside.
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Re: SDs and micro SDs

Sat Jan 03, 2015 3:55 pm

MicroSDs are even cheaper without the adapter. I've got a pair of spare adapters so will just be buying 8GB microSDs for the next couple of projects.
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Re: SDs and micro SDs

Sat Jan 03, 2015 4:16 pm

jamesh wrote:I think a 8GB card is a sensible size vs price compromise.
+1

Even if James and I are somewhat notorious for not agreeing ;)

You can't really argue with the swag store offering at 4 quid.
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Re: SDs and micro SDs

Sat Jan 03, 2015 4:40 pm

pluggy wrote:
jamesh wrote:I think a 8GB card is a sensible size vs price compromise.
+1

Even if James and I are somewhat notorious for not agreeing ;)

You can't really argue with the swag store offering at 4 quid.
Tell you what, I'll agree with you when you are right, and you can agree with me when I am right.
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Re: SDs and micro SDs

Sat Jan 03, 2015 4:43 pm

pluggy wrote:You can't really argue with the swag store offering at 4 quid.
Except that one is showing as "out of stock" at the moment.
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drgeoff
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Re: SDs and micro SDs

Sat Jan 03, 2015 4:53 pm

I expect that when the OP finds his misplaced spectacles he will confirm that the SD card is indeed an adaptor with a micro-SD inside. :)

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Re: SDs and micro SDs

Sat Jan 03, 2015 5:14 pm

BMS Doug wrote:Class 4 or class 6 cards are better for use with a pi than class 10 cards.
Why? Storage performance seems very important for having a system that feels snappy in use. My new B+ has a class 4 card whereas my old B has a class 10 card. The new B+ feels very sluggish. I would say that the difference in responsiveness is greater than any CPU overclocking could achieve.

Is there still some reliability issues with Pi's SD card performance that makes the slower cards the better choice?

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Re: SDs and micro SDs

Sat Jan 03, 2015 5:34 pm

The class has nothing whatever to do with the read performance of a card. The read speed which is what matters is usually much faster than the write speed which is what class is about. Class 4 and class 6 cards are often (but not always) faster than a class 10 when it comes to reading. At best, a Class 10 is just a waste of money but theres a fair chance it could be slower. The Sandisk class 4 I use read at around 20-22 MB/s although it writes at about 4 (hence class 4) a Class 10 might only read at 12 MB/s although it writes at 10. The extra performance in writing is completely lost in everything else happening (slowly) on the Pi.
Last edited by pluggy on Sat Jan 03, 2015 5:42 pm, edited 1 time in total.
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Re: SDs and micro SDs

Sat Jan 03, 2015 5:39 pm

a card optomised for the best write speed is not needed for the pi, see the sd card benchmarks thread here
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rpdom
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Re: SDs and micro SDs

Sat Jan 03, 2015 5:44 pm

A few of the more expensive class 10 cards do work better than the rest. They seem to work better on small random read/write as well as large continuous access, however I've seen performance tests on a Pi which show that there is little difference between an ordinary class 10 and a reasonable (not cheap) class 4 or 6 for small random writes. Some of the c10's were slightly faster than some of the C4s and vice versa.

I've noticed that cheap C4s can be a lot slower than a good C4 as well.

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Re: SDs and micro SDs

Sat Jan 03, 2015 6:04 pm

pluggy wrote:The class has nothing whatever to do with the read performance of a card. The read speed which is what matters is usually much faster than the write speed which is what class is about. Class 4 and class 6 cards are often (but not always) faster than a class 10 when it comes to reading. At best, a Class 10 is just a waste of money but theres a fair chance it could be slower. The Sandisk class 4 I use read at around 20-22 MB/s although it writes at about 4 (hence class 4) a Class 10 might only read at 12 MB/s although it writes at 10. The extra performance in writing is completely lost in everything else happening (slowly) on the Pi.
Night and day between my Class 10 Samsung SD card and Class 4 Kingston MicroSD card, in favour of the Samsung. So it was not a waste of money at all. Although I didn't choose it because of the class rating but because of the reported read speed. So, instead of buying class 4 or 6 cards, I would recommend to check what is the the card's read speed in megabytes per second as reported by the manufacturer. I suspect that big companies as Samsung, Sandisk , Kingston and Transcend do report their speeds accurately. If you can not find the speed reported anywhere, do not buy the card - because most probably it is a slow card.

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Re: SDs and micro SDs

Sat Jan 03, 2015 6:13 pm

BMS Doug wrote:a card optomised for the best write speed is not needed for the pi, see the sd card benchmarks thread here
Isn't the problem with all of those benchmarks the same as with every benchmark. Benchmarks are only good for showing how a system performs while running a benchmark rather than running any realistic workload. We all have to admit there's a field full of male bovine excrement written about the whys and wherefores of SDCards and the RPi.
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Nick Keighley
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Re: SDs and micro SDs

Sun Jan 04, 2015 2:27 pm

indeed the SD card was in fact a microSD adaptor (which the Pi Shop's customer services kindly pointed out to me). Thanks for the replies.

Ah well...

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