Does extra hard drive cache make a difference for streaming video?

Question

I am looking at the following two drives for a RAID device, which will be streaming normal things but also a lot of video:

• Seagate Constellation ES.3 ST4000NM0033 - hard drive - 4 TB - SATA-600
• TOSHIBA DT01ACA300 3TB 7200 RPM 64MB Cache SATA 6.0Gb/s 3.5"

Will the 128 MB cache on the Seagate have an effect in my described scenario, compared to the 64 MB on the Toshiba? If so, what sort of difference can I expect?

I'm using a qnap device, if that matters.

Solution

From what I understand, a hard drive cache is used for stashing frequently accessed information in a fast solid state buffer (cache) on the drive so when that particular data is requested again the drive can pull it out of cache- a much faster process than getting it from the mechanical part of the drive. If you are streaming movies (or video) there probably won't be any performance advantage with a larger cache, since the same data won't be accessed repeatedly. Having said that, all things being equal, there is no downside purchasing a drive with a larger cache, and it might help with some of the smaller 'normal' files you refer to.

Comments

[HikeMike]

Nobody here can tell you whether it's worth your money (except if the more expensive drive is worse in every way, but let's not assume that). You could try asking how to determine which drive is best for your use case instead, not asking for specific models...

[Ng Zhong Qin]

@DanielBeck I thought I did.

[Ng Zhong Qin]

I asked for video with the device specifically if 128MB cache was better than 64MB cache in the hard drive. Is it hype or a real difference worth the extra money.

[BobT]

I'm not sure why this was closed... It seems to me to be a legitimate hardware question, i.e. "Does extra HD cache make a difference when streaming video". We can at least present the pros and cons of large caches. He can decide if it's worth the extra cost...

[Ng Zhong Qin]

@BobT Once a question gets hit for closing people jump on it. I've selected another forum but I was hoping for here.

[Indrek]

I removed the shopping-related parts from the question, including the prices, to make it purely about the effects of HDD cache. @johnny If you think I removed too much, do feel free to rollback to a previous revision. I also voted to reopen.

[Ng Zhong Qin]

@Indrek Thanks. I don't think anyone cares anymore since the question is older and closed, but maybe it will get opened.

[Reality Extractor]

I am reasonably sure that this explanation of what the cache on disk does is incorrect. The drive cache holds IO operations, not frequently accessed data. More cache = more IO ops that can be queued and reported to the OS as completed regardless of whether they were already written to disk.

[Johannes]

I agree with Extractor. I think what Bob is describing would be hybrid 'SSHD' drives that have actual solid state storage for storing frequently accessed information. The SSD on these hybrid drives is typically several Gigabytes in size, and are separate from the actual cache.

[Jamie Hanrahan]

Sorry, but the above two comments are definitely incorrect. The cache contains data from recent operations, not a queue of commands. The difference with a hybrid drive (SSHD) is that the SSD part of the cache is persistent across power-downs, and therefore can be used to improve e.g. boot times, while the usual onboard cache is RAM, and therefore volatile.

[Jamie Hanrahan]

SSHDs don't necessarily store "complete files". They might do so, but if they do, it's only by happenstance - and the same for the RAM cache on HDs, and the same for SSDs. Drives (all types) have no idea what a "file" is; the read and write commands sent to the drive refer only to logical block numbers. All "file" semantics are implemented in the host OS's file system driver; the drive is completely unaware of them. And drives have no way to associate IOs with "the front of a file" either.