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UHC-II in one slot, UHC-I in the other... downsides?


boldblue737
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I'm primarily a stills shooter and don't plan on doing a lot of video with the X-T4, all my existing SD cards are UHC-I San Disk 170 mb/s cards. With my new XT-4 body I do want to get a UHC-II card to ensure I have maximum burst rate and I suppose if I ever shot a bit of video I don't want issues. I was unaware of how pricey UHC-II cards are so here is my question...

Can I buy a 128GB UHC-II San Disk Extreme Pro 300 mb/s card for slot 1 and then use one of my 128GB UHC-I cards in slot 2? I know the answer is YES, however what are the consequences? If I set the camera to "backup" to slot 2 (my "slow" card) will that impact burst rate or video features to slot 1 (my fast card) or since it is just a backup will the camera just get to it when it gets to it? What if instead I have RAW files go to slot 1 (my fast card) and JPGs go to slot 2 (my "slow" card)... will that impact speed of burst since I would assume the smaller JPG files wouldn't tax the slower card as much? OR do I forget this all and the only way I take advantage of UHC-II speeds to either only use a single UHC-II card (with NO card in slot 2) or just bite the bullet and buy two UHC-II cards?

Thanks everyone!

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I have used UHS-II in one slot of the X-T3 and UHS-I in the other but shoot in sequential mode so the UHS-I would only be used if the first slot fills.

If you shoot in backup mode the camera will write at the speed of the slower card.

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12 hours ago, Greybeard said:

I have used UHS-II in one slot of the X-T3 and UHS-I in the other but shoot in sequential mode so the UHS-I would only be used if the first slot fills.

If you shoot in backup mode the camera will write at the speed of the slower card.

Thanks, that pretty much is what I thought.

With how little I plan on shooting video, a single SD card of 128 GB is plenty for even a week long trip for me... so my current plan is to just use a single card (300 mb/s UHC-II SanDisk Extreme Pro). At some point in the future if I'm on a "dream" trip or something where I am uncomfortable with any risk I'll invest in a second UHC-II card in backup mode, but for now I'll just use one.

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Posted (edited)

Ok a bit of an update here. It appears that IF you set Slot 1 (with your fast UHS-II card) to record RAW and Slot 2 to record JPG (with your slower UHS-I card) there shouldn't be any or any significant slowing of write speed or at least not as big a hit as you'd think. Way back in 2017 someone tested this issue with the XT-2 and found that as long as you set slot 1 to record RAW to your fast UHS-II card and slot 2 to record JPEG to your "slower" UHS-I card which  was 95 mb/s+ (they tend to top out around 170 mb/s and are super cheap now) the write speed would be identical in terms of when the camera paused burst images. In the case of the XT-2 basically I think after about 116 burst shots it would stop... no mater if the second card was a UHS-II or not because writing the much smaller JPGs didn't create the bottle neck first. Now if they reversed the cards and tried to record the RAWs to the UHS-I card and the JPGs to the fast card it hit a bottleneck at around 56 shots. 

Basically it seems when splitting RAW/JPEG you can get away with using the slot 2 with a slower UHS-I card without impacting burst speed and more than if the cards were both UHS-II. For me this is acceptable because it allows me to use slot 2 as a "backup" of JPGs (a worthy tradeoff to save the money of another large capacity UHS-II card to get a true RAW backup there). I suppose with the XT-4 which has slightly larger RAW and JPEG files than the XT-2 this could have changed slightly but I doubt it with improved CPU performance etc. I think the other eye opener is that the XT-2 did 56 burst shots in a row before stopping even with the SLOWER card, so assuming you don't want to do high bit rate video all but the most diehard sports photographers have no real reason to buy a UHS-II as the burst performance is still pretty darn good.

1. Using slot 2 to record JPG with a UHS-I is a reasonable solution to saving money, creating a form of backup (although not a RAW backup) and without impacting burst performance.

2. If you don't intend to shoot high bit rate 4K video, it may be more than acceptable to use ALL UHS-I cards for most photographers as while burst rate drops quite a bit, it still is far more than most folks would find themselves requiring.

3. The fastest burst rate is ALWAYS if you shoot ONLY raw to a single card with NO recording of a backup or JPG to another card. Just 1 RAW to 1 UHS-II card. That's the fastest of all.

My final solution was to put a $145 128GB 300 mb/s UHS-II card in slot 1 for RAW (3900+ compressed lossless photos + video is dedicated to this slot) and a $30 170 mb/s UHS-I card in slot 2 for JPG (7700+ JPG photos).

Here is the link to the experiment: https://www.fujix-forum.com/threads/raw-jpeg-slower-card-in-second-slot.66119/

Edited by boldblue737
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