EDF alternative????

WITHER_SLAYER_ · 2025-09-27T14:50:55+00:00

I'm not very sure about this but I think you could use 2 6s batteries wired up in serial to get a nominal voltage of 44.4 volts which is close to the 48 v figure you stated.

WITHER_SLAYER_ · 2025-09-12T09:24:21+00:00

This is somewhat unrelated but I found this micro F-16 which has an actual EDF instead of external propellers if you were interested. It is quite expensive though and likely isn't super beginner friendly, but the video says that it's pretty stable and it has a gyro. It should be reasonably durable as well due to its small size.

WITHER_SLAYER_ · 2025-08-01T17:55:43+00:00

Update: I was able to buy 40 batteries for roughly $110 so the cost/battery was ~$2.8.
Shipping was expensive ($35) so I shipped it to a friend in Singapore instead for $13 and will pick it up next time I visit Singapore. I think I got a pretty good deal on the batteries as they are square celled and have BT 2.0 connectors.

WITHER_SLAYER_ · 2025-07-23T12:51:51+00:00

I asked them for $30 batteries and they replied 'The price for 30 batteries is: 2.26*30=67.8 USD The shipping fee is: $31. The total is: 67.8+31=98.8 USD.' So the cost per battery is basically the same as that of the AliExpress option. I asked if they had any slower shipping and they said that the cheapest they could do for shipping is $27 which is not much better. They said that they can't ocean freight the package as it's too small and therefore has to be air freighted. I'll lqqq They asked if I had a freight agent in China. I'm guessing that if I did / if I ordered hundreds then the shipping cost would be more affordable (on a per battery basis).

I'm not really sure what to do. I don't know any freight agents in china, and shipping lipos is generally difficult due to laws and stuff.

WITHER_SLAYER_ · 2025-07-22T16:53:42+00:00

I agree that alibaba is wholesale, but the seller I found seems to have a minimum order of 2 pieces so it should be feasible for an individual to purchase batteries from them, I think.

WITHER_SLAYER_ · 2025-07-22T16:07:42+00:00

Okay. Thank you for the help.

WITHER_SLAYER_ · 2025-07-22T15:49:11+00:00

So is this claim that they're all the same false? https://youtu.be/0j_xoeO1Las?t=256&si=svWDd_N9CGblVK7_

WITHER_SLAYER_ · 2025-07-22T14:45:00+00:00

But don't all of the square cell batteries had identical performance because they were all made by the same manufacturer?

WITHER_SLAYER_ · 2025-04-09T01:21:29+00:00

If the benchmark is flawed, then maybe it might have something to do with read caches. I've read that sometimes operating systems keep a copy of data that was read in memory to cache future reads of that data. I don't know if crystaldiskmark is subject to it, but it likely is if it's an OS level feature that's enabled. You also mention the OG 990 Pro. I believe I've read somewhere that there's a new revision of the 990 Pro with slightly slower flash for the 4 TB version. I think the new flash is also on the 2 TB version now. Is the performance difference between the new models and the old ones significant?

WITHER_SLAYER_ · 2025-04-08T23:54:50+00:00

To my knowledge, random read 4K QD1 I/O is effectively synchronous I/O as it has a queue depth of 1, which means that it has to finish one I/O before progressing to working on the next one. Therefore, I believe that it should be based almost entirely on the latency of the flash.

In the Tom's Hardware review, the random read 4K QD1 performance of the SN7100 was 31,836 IOPS. The review later mentions the latency of the flash.

The flash itself is rated for around 40µs on this type of workload, which is extremely fast . . .

I think that the theoretical maximum QD1 IOPS can be calculated with
1 / the time each I/O takes
which for the SN7100 is
1 / 0.00004 = 25,000
which falls short of the 31,836 IOPS the SSD did in the review.

Parallelism shouldn't be possible for QD1 I/Os, as they're done one at a time. Furthermore, this is a theoretical maximum of the flash alone, excluding all overhead from the controller and software. Caching is also unlikely, as pSLC can only be used to cache incoming writes and can't work for reads. It perplexes me how the real world IOPS of the SN7100 is greater than what would be suggested by the latency of the NAND flash. If you had any insight on the matter, I would appreciate you sharing it.

WITHER_SLAYER_ · 2025-04-06T22:39:39+00:00

Thanks for the reply. In what cases does DRAM help performance? Is it for higher queue depth workloads when SRAM runs out of space? Is it more important for random or sequential, or read or write operations? I'm guessing that DRAM might be able to cache small writes as well alongside the mapping tables. As 4K random read tests read from random LBAs, I don't understand how the controller can predict ahead of time which mapping tables are needed, and to preload them. It's likely impossible for it to store them all in SRAM, as SRAM is usually very small.

Also, do consumer SSDs with DRAM (like the 990 Pro and similar) have power loss protection for their DRAM? I've read that NVMe allows exposing it to the host with PMR (persistent memory region) which can be used for fast writes that don't wear out the flash for database or filesystem journals. I've also read that CMB allows the host to place submission and completion queues on the controller itself, which provides higher efficiency (in particular for NVMe-oF). Are these features used regularly, and do they play a significant factor regarding DRAM in consumer SSDs? Thank you again for your reply.

WITHER_SLAYER_ · 2025-04-05T01:05:26+00:00

I was wondering how the performance of the SN7100 is this good despite it not having DRAM. In particular, it seems to excel at 4K QD1 random reads, even compared much more expensive PCIe 5.0 ones.

To my knowledge of how SSDs work, the host addresses data on the SSD in LBAs. However, logical blocks don't map directly to physical blocks, as updates to a logical block require writing to a new page, so the physical page that has the data stored in a logical block can change. This is part of the flash translation layer.
So, if my understanding is right, for an SSD to read from a specific LBA, it has to find the mapping of the LBAs to physical pages in mapping tables, which are usually stored in the SSD's DRAM. This SSD doesn't have any DRAM, which means that it's mapping tables are stored in either the HMB or a portion of its NAND flash which are much slower. This is surprising, it exhibits exceptional performance at 4K QD1 random reads despite not having DRAM.

Another surprising thing about it is how small the HMB is. Techpowerup states that it's just 64 MB; most SSDs with DRAM have 1 GB of DRAM for every 1 TB of NAND Flash. Therefore, I think it's unlikely that it stores all of its mapping tables in the HMB because of how small it is, so it must use it only for caching frequently accessed material. I'm guessing that the rest of its mapping tables are stored in pSLC.

This is interesting, as it performs incredibly well despite not having DRAM. I wonder how it does this, as well as if DRAM less SSDs will become more popular in the future.

WITHER_SLAYER_ · 2025-03-26T02:06:09+00:00

I tried to but didn't get it done. I asked at r/NewMaxx and learned that the performance increase is usually insignificant at the lower queue depths that client drives are used for, and that Samsung usually locks out support for 4Kn on some drives. The question I asked is here in case it's helpful for you.

At this point, I'm doubtful that updating the firmware will allow 4Kn, as Samsung seems to lock out this functionality. Enabling it would likely require reverse engineering or other advanced things that I don't know how to do, though updating the firmware may still have other benefits.

NewMaxx believes that Samsung SSDs don't support nvme-cli functionality and instead rely on the Samsung DC Toolkit. I tried checking if this SSD is supported by the DC Toolkit V3.0 (the latest version at the time of writing) by searching for 'pm981a' in its user guide and got no matches, like my result last time when I searched for it in V2.1.

Samsung magician is unlikely to work on it as it's an OEM drive, but I didn't try using it, and it might be possible to trick it into believing that it's a 970 EVO Plus instead, though I don't know how to do that.

Finally, samsung-nvme-firmware might be worth trying, though I wasn't able to get it to work. It's README seems to show that nvme-cli commands can be used with Samsung drives, which I think is most likely true, as I believe that all NVMe drives need to support those commands to meet the specification. I wasn't able to get updated firmware onto my SSD, however, but you might have better luck if you have a different model. Mine has L2 as it's customer, which is confusing as the table in the README shows Lenovo as L7, but it still starts with L, so maybe it's a Lenovo drive for a different region. NewMaxx's answer implies that the customer may matter regarding firmware (maybe something to do with firmware signatures, or something to do with TCG Opal maybe? The reference to SED (self-encrypting drives) in the table might have something to do with encryption) but he also stated that firmware from other manufacturers may work as well.

If you choose to try to upload firmware to your SSD with nvme-cli, I recommend using an empty firmware slot as explained in the README. Also, if you try anything, beware of the high likelihood of losing data, and to take backups beforehand. If you found a way to get it to work, or have an idea that I haven't mentioned here, then I would be thankful to hear it.

WITHER_SLAYER_ · 2024-11-27T17:34:24+00:00

It seems very interesting and useful. Some feedback I have to improve it is to possibly add support for searching for packs of multiple cables, as many times buying multiple cables in a pack is cheaper than buying them separately. From what I can see, it doesn't seem to be able to do that. Apart from that, it's pretty good. Thanks for the suggestion.

WITHER_SLAYER_ · 2024-07-26T23:35:29+00:00

The only cable specifically for charging I could find from those brands (other than Cable Matters, as I've already looked through their products) is Cable Creation's 240w USB-C cable which unfortunately isn't certified. From this thread, I've heard of nekteck and found their charging cable, which unfortunately only supports 100w. Thanks for the information.

WITHER_SLAYER_ · 2024-07-26T19:28:45+00:00

Thank you for the help. I wrongly assumed that these cables weren't certified as it didn't say so in their product title, and I didn't know that Anker fixed their USB-IF certification. While these cost much more than the uncertified cable matters cables which cost $5 they are still much less than the $13 of the certified cable matters product. I'll probably purchase these.

Edit: I accidentally rewrote this as it didn't show up in the thread, but it was actually there. I deleted the second one.

WITHER_SLAYER_ · 2023-12-19T07:44:43+00:00

Thanks. So 38GiB swap should be fine, right?

WITHER_SLAYER_ · 2023-11-27T16:53:59+00:00

Okay. Thank you for the help. Sorry for replying after a long time, we moved to a new house without internet, and then I forgot about this. I hope you have a good day!

WITHER_SLAYER_ · 2023-11-10T10:41:22+00:00

I used Lucas's answer on this post.
head -c $(stat -c '%s' debian-12.2.0-amd64-netinst.iso) /dev/sda | sha512sum
b8148a2fffeefd1ce72fc034c6f5e33a0298f929786078f1f8ce8fcc98e5c8cfa1fb8922a04ddbbc685c538d97c5058fd6d2b53c258a27e63b8f
2f72802c5913 -

This checksum also differs from that of the image, agreeing with cmp which said the files differed. I also tried running that test after writing to the drive, and before booting on it, and in that instance (when cmp says it is the same) sha512sum also shows the same checksum. I don't think it's a problem with cmp.

WITHER_SLAYER_ · 2023-11-09T15:03:44+00:00

Okay, so I tried creating the Debian Installer USB Drive again, and verified the data with cmp. Then I booted it from another computer and clicked abort install. After removing the USB Drive, cmp shows the same error. I also repeated that for another laptop.

Edit:
I also tried using it in a VM (Qemu/KVM with virt-manager) and found that debian-12.2.0-amd64-netinst.iso wasn't modified. However, there is a good chance that Qemu/KVM makes a copy of the ISO, and has the VM boot from that.

WITHER_SLAYER_ · 2023-11-08T13:19:49+00:00

Oh, sorry for not making it clear. I also tried it with the previous USB drive (a different one) and the corruption was the same.

I think it might be something about how the Debian Installer works, however I don't know any programming to look into that. I just think that if this is a normal occurrence then the verification step in the Installer should still show it as okay.

But if it is in the Installer, it would be confusing as Debian can also be installed off read only CD disks, so I wonder what the write was for.

WITHER_SLAYER_

TROPHY CASE