The iPhone 17 Pro and Pro Max past twelvemonth introduced a 2TB retention tier. Just similar them, the iPhone 18 Pro and iPhone 18 Pro Max are disposable successful 4 configurations: 256GB, 512GB, 1TB and 2TB. Something has changed, however, and it is the benignant of retention used. In a video connected BiliBili, Homolab compared 2 18 Pro Max phones, 1 with 512GB retention and 1 with 1TB.
Apparently, the 256GB and 512GB Pro models usage TLC flash – each representation compartment fits 3 bits. However, the 1TB and 2TB models usage QLC – 4 bits per representation cell. QLC is known to beryllium slow, truthful Apple added a accelerated SLC cache (one spot per cell), followed by a TLC cache and past the QLC bulk storage.
That works good until it doesn’t. In the tests, the SLC cache could prolong constitute speeds of up to 3,000MB/s. But erstwhile it’s filled up, the telephone starts penning to its TLC cache, which is slower but inactive respectable astatine 578MB/s. And erstwhile some levels of cache are full, the telephone goes to the QLC retention that lone manages 79.4MB/s with dips to 25.6MB/s.
This is portion the retention is empty, erstwhile the SLC cache is 250GB. But erstwhile retention starts to capable up, the size of the cache shrinks – astatine 60% retention used, the SLC cache is lone 58GB. The TLC and QLC memories get likewise filled up and they go slower too.
Homolab’s measurements astatine 60% retention utilized amusement 396MB/s for the TLC cache and an abysmal 1.1MB/s for the QLC storage. Again, this is for sustained writes.
There is simply a quality successful random entree too. The 1TB iPhone 18 Pro Max with QLC was 38% slower successful 4K random reads than the 512GB TLC model. This is astatine debased queue depths. Once much processes commencement requesting information from the storage, the QLC exemplary closes the spread to 12%, but it is inactive slower than its TLC counterpart.
Normally, flash retention gets faster arsenic its capableness grows arsenic the workload tin beryllium divided betwixt antithetic NAND chips. However, this lone holds existent erstwhile comparing retention similar for like. SLC is the fastest, but it’s expensive. MLC, TLC and QLC battalion much bits per chip, truthful they outgo little for a fixed capacity, but the trade-off is their little speed.
Anyway, these are synthetic tests and it remains to beryllium seen what the real-world interaction of utilizing QLC for the priciest iPhone models volition be. And yes, the iPhone 17 Pro and Pro Max utilized TLC adjacent astatine the 1TB and 2TB tiers. Of course, that was earlier representation became much costly than gold.
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