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SSD portion of hybrid drives

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June 11, 2013 10:25:46 PM

I thought the SSD portion of a hybrid drive was generally from 4-128 GB. Why are they being listed all over with statements about cache in MB (three orders of magnitude smaller)? If that is something different, why is the SSD size not listed?
a c 108 G Storage
June 11, 2013 10:39:59 PM

A standard HDD usually has a cache of 8-64MB. A Hybrid HDD usually has a NAND cache in the tens of GB.

You may be mixing up your acronyms.
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June 11, 2013 11:13:00 PM

Ok, cache is not NAND cache, but I saw some hybrid drives listed with 32 and 64 MB cache, and no size spec for the SSD portion. Do the hybrids have two cache types, and wouldn't the SSD NAND cache be most important to list?
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Related resources
a c 108 G Storage
June 11, 2013 11:14:42 PM

They have both RAM and NAND cache - the RAM is stuff ready to go from/to the SATA port, the NAND is long-term storage.

What drive? Link?
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a c 108 G Storage
June 12, 2013 7:55:17 PM

Interesting - my guess is a combination of people looking for cache sizes because it's what they've always done, and Seagate/WD not wanting to be compared in respect to the exact amount of NAND. Probably only 4GB.
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June 14, 2013 10:34:41 AM

Thanks for the doc. Any pointers to the 32Gb NAND drives?

I seem to remember some discussion re 64Gb NAND hybrid drives and larger (Don't remember where). Maybe someone will design a routine to log, analyze, and profile caching patterns. But, until various user groups are sampled, some will buy too little NAND, and others will buy more than they need.
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June 20, 2013 8:29:42 PM

" Any pointers to the 32Gb NAND drives? "

Anyone using a hybrid drive? Seagate Momentus drives are apparently popular lately, but what about the Western Digital models (different system, I read)?

I am thinking about a 500 GB drive: What model is recommended (brand and #)? What size is the NAND ram?

Regarding Seagate switching to 5400 rpm for the spinning portion: Do they choose that because it is faster to spin up to 5400 rpm compared with 7200 rpm (while letting the NAND portion do the speedy caching)?

If one tends to save open files frequently, in case the machine or program crashes, will this significantly use up the SSD life (using write cycles)? Imagine working frequently in some spreaadsheet files and saving frequently.

I like the Seagate strategy to encourage letting the firmware manage what and when goes to the HDD and what and when goes to the SSD. It sounds like WD will allow (require?) more interaction, but it seems best to use some automatically tuning algorithm. Any thoughts on this?
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December 10, 2013 9:08:24 PM

This is an marketing issue! They use cache to replace buffer in datasheet which looks more advanced.

Usually, the cache (usually size between 8MB to 64MB) are buffer which provides read-ahead and read-behind buffering. The SSD cache in SSHD is firmware-based cache focus on sector-track. The file cache managed by operating system or those need a drive focus on files. You may use a file but doesn't need to read the full file content. that's what firmware-based and software-based cache different.

There is an explain on Buffer and Cache in Hard Drive and Operating System explains the SSD Cache Size of your SSHD shall help you to understand the internal story and size matters.

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