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SD card capacity

RonAndres

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#1
I just bought a 128GB microSD card Samsung Evo Select. Do you think that card is a good choice for a Mavic Air? Is it too big?
 

BD0G

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#3
  • Size: Generally speaking you don’t want to buy a super high capacity card for your Mavic Air. We find that 32gb or 64gb cards work the best and we generally prefer multiple 32gb cards. Anything over 64gb is overkill as you’ll store too much on the card. Using 32GB cards forces you to change the memory card with each battery change. Shooting in 4k will take a large chunk of a 32gb card on a 20 minutes flight. This way if you do crash or lose your drone you’ll only lose the footage from that flight and not all the ones before it!
Source: Mavic Air: The Best SD Memory Cards
 

CanadaDrone

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#4
I just bought a 128GB microSD card Samsung Evo Select. Do you think that card is a good choice for a Mavic Air? Is it too big?
That is more than enough - that is a little under 3 hours of video and your batteries last about 15-16 minutes before 30% RTH.

For the Mavic Air, every 15 minutes of footage is ~11.3GB.

Assuming you have the fly more combo, if you run through all 3 batteries you're looking at a tiny bit more than a full 32GB card, which was my reasoning for getting 64GB cards. Plus 64GB cards are absolutely dirt cheap.

128GB is lots. It's not too big, just make sure you backup/offload your important footage so all your eggs aren't in one basket if something goes wrong.

More importantly, the card needs to be V30/U3 certified to guarantee a minimum sustained write speed fast enough for the 100Mb/s (12.5MB/s) of the Mavic AIr. Samsung makes different versions of the Evo Select and some are too slow - if it's U1 it's too slow, if it's U3 you're good to go.

Really try to ignore any "lists" or fancy labeling like "extreme" on memory cards - the only thing that matters for you is the minimum sustained write speed which is rarely if ever advertised, but it is denoted by the U3 / V30 / V60, etc. labeling.
 

FoxhallGH

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#7

CanadaDrone

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#8
The fastest data transfer is on the cards with the U symbol, with the number 3 in it i.e. like the 64 EVO Select on the left.
Useful article regarding the choice of SD cards here ... https://www.adorama.com/alc/7809/article/picking-right-sd-card-what-do-numbers-mean
Yes that is what I explained in my first post ;) I am trying to make people aware of the minimum sustained speed ratings as it is often overlooked or wrongly equated with maximum instantaneous write speeds.

So many people say "oh I have a sandisk extreme (or whatever), and it works great." That means *nothing* as there are so many different versions and the manufacturers play around with naming schemes in different card qualities. People need to be aware of the labeling and the minimum sustained write speeds, which manufactures do not actively advertise.

I have a much longer write up on memory here if you're curious:

Tips for New Flyers
 
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FoxhallGH

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#9
Yes that is what I explained in my first post ;) I am trying to make people aware of the minimum sustained speed ratings as it is often overlooked or wrongly equated with maximum instantaneous write speeds.

So many people say "oh I have a sandisk extreme (or whatever), and it works great." That means *nothing* as there are so many different versions and the manufacturers play around with naming schemes in different card qualities. People need to be aware of the labeling and the minimum sustained write speeds, which manufactures do not actively advertise.

I have a much longer write up on memory here if you're curious:

Tips for New Flyers
Thanks for the reference - Yes - we are in Violent agreement on that one :) ... I was just concerned that the posted illustration gave prominence to the 128Gb U1 card ...
 
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CanadaDrone

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#10
Thanks for the reference - Yes - we are in Violent agreement on that one :) ... I was just concerned that the posted illustration gave prominence to the 128Gb U1 card ...
Yes - sorry for the confusion. I did that on purpose - I was trying to show that the exact same card is manufactured with two very different minimum sustained write speeds, so when someone else says "I have a Samsung Evo Select and it works great!" someone might go out and buy a U1 version and it won't work. Very rarely are people specific enough in their memory card recommendations, and the manufacturers don't make it easy on the customer.

Above the images I posted, I mentioned that one is too slow, one is OK as a caution.
 
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Meta4

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#11
I just bought a 128GB microSD card.
Is it too big?
The most common idea seems to be bigger must be "better", but to my way of thinking, 128GB is much, much too big.
128GB will hold about 4 hours of 4K video.
That's >8 flights if you wanted to record every second of each flight (why would you?)
Or more photos than you could take in a couple of weeks.

The way to tell if it's too big is to ask yourself how much of your work you are prepared to lose at one time.
Since I value my work, 16GB is more than big enough.
I swap SD cards when I swap batteries and none of my work gets sent out on a second flight.
 
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vanderzyde0

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#13
I made the mistake of mixing up MB and Mb per second

Remember that MB = Mega BYTES and Mb = Mega BITS

The MA writes at 100 Mega Bits (Mb) per second

The U3 memory card above is rated at 60 Mega Bytes (MB) per second

So the card is at least 4 times as fast as it needs to be

According to specs a U1 card should also work-

Up to 95MB/s & 20MB/s read & write speeds respectively; Class 10 UHS 1

20 MB/s is about 160 Mb/s

Anyone have any issues with U1 cards?
 
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#14
I use several of the Samsung 64 EVO U3 cards and swap them between my drone and my digital SLR camera. They work fine in both. There's nothing wrong with the 128 GB card but like others have said, you'll probably never fill it up.
 
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CanadaDrone

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#15
I made the mistake of mixing up MB and Mb per second

Remember that MB = Mega BYTES and Mb = Mega BITS

The MA writes at 100 Mega Bits (Mb) per second

The U3 memory card above is rated at 60 Mega Bytes (MB) per second

So the card is at least 4 times as fast as it needs to be

According to specs a U1 card should also work-

Up to 95MB/s & 20MB/s read & write speeds respectively; Class 10 UHS 1

20 MB/s is about 160 Mb/s

Anyone have any issues with U1 cards?

It's not quite that simple, but you're right that it is easy to mix up MB and Mb and people do it all the time.

You do not want to use any U1 card with the Mavic Air, or any of DJI's drones that shoot at 100Mbps which is most of them now.

100Mbps is 12.5MB/s.

You are confusing one very important thing though - the cards rated speed is *not* it's minimum sustained write speed. When card manufacturers say "up to 100 MB/s" (or similar), that is almost always the instantaneous maximum read speed. Maximum write speed is almost always lower, and more importantly, minimum sustained write speed is almost always a lot lower. Minimum sustained write speed is never advertised beyond the symbols on the card, so it is extremely confusing for consumers who don't fully understand all the SD card ratings and symbols.

A U1 card means the minimum sustained write speed is only 10MB/s, so it is too slow for a Mavic Air which writes at 12.5MB/s. You want to give yourself some headroom too, so that is why we go with U3 cards (30MB/s minimum sustained write speed). There are no U2 cards.

Class 10 also just means minimum sustained write speed of 10MB/s, which is too slow. Almost every card has this symbol so you can pretty much ignore the "class" ratings because they don't go beyond 10 and 10 is too slow.

The only thing that matters is that you see a "U3" or "V30" (or higher) symbol on the card, both of which mean minimum sustained write speed is 30MB/s.

If you look at the manufacturer's advertised speeds, those are NOT minimum sustained write speeds, but theoretical instantaneous maximums, and almost always refer to read speed not write speed, which again does not matter for our purposes.

And lastly, you can ignore the UHS (bus speed) ratings. Those are the roman numerals on the card (either I, II, or III). The Mavic Air's card slot is UHS I and it is more than fast enough (up to 104MB/s or 832Mbps). If you do have a UHS II card though, they are backwards compatible so it will work, it just isn't necessary to pay the premium for one.

More info in my write up here:
Tips for New Flyers
 
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vanderzyde0

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#17
OK 100 Mb/s for 4K video at 30 fps

What about 1920x1080?

Doesn’t the write rate vary based on information entering the CMOS?
 

FoxhallGH

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#18
OK 100 Mb/s for 4K video at 30 fps

What about 1920x1080?

Doesn’t the write rate vary based on information entering the CMOS?
The following is an extreact from: https://www.adorama.com/alc/7809/ar...d-what-do-numbers-mean?utm_source=rflaid64367

SD cards are available six different speed classes, from slowest to fastest: Class 2, Class 4, Class 6, Class 10, U1, and finally U3. U1 and U3 cards are compatible with the UHS transfer bus used in newer devices, so you will often see a card rated with both U1 and Class 10. That means that when the card is used on a standard high-speed data bus, it will perform at Class 10 speed, but when used on a UHS bus, it will perform at U1 speed.

Class 2 – these cards are the slowest class currently available and are best suited for consumer-level point-and-shoot cameras, audio recording, and low-resolution SD video recording.

Class 4 & 6 – the “middle of the road” in terms of speed, these cards will work well with still cameras shooting jpeg files, and some very light HD video recording at 720p.

Class 10 & U1 – these cards are capable of recording at up to 10 MB/s, so they are well suited for pro-level still cameras shooting RAW photos, and HD video recording at up to 1080p. This is a great speed to purchase if you’re looking for a balance between compatibility with your current equipment and future usage as well.

U3 – these cards are overkill for most uses, but are absolutely crucial if you’re shooting 4K video with your device. 4K video files are large, and require a card with a high sustainable speed to be able to write them properly. U3 cards are quite a bit more expensive than the slower speeds, but if you need them, you really shouldn’t risk using anything slower.
 

CanadaDrone

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#19
OK 100 Mb/s for 4K video at 30 fps

What about 1920x1080?

Doesn’t the write rate vary based on information entering the CMOS?
Still 100Mbps maximum.

1080P @ 120FPS is still 100Mbps, but when you play it back in slo-mo 30FPS (120 / 4) it is 25Mbps (100 / 4). If you play it back at 120FPS it is 100Mbps and it is recorded at 100Mbps.

The bitrate is the amount of data given to each second of video measured per frame. The higher the bitrate, the higher the quality all else equal. File size is simply the bitrate X duration.
 
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