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I've always been taught, and know from experience, that as far as performance goes (i.e., speed or raw read/write) RAM is always waaay faster than a mechanical hard-drive. But where do Solid-State Drives fit into this spectrum? Are they faster than mechanical hard-drives? Much faster? Are they as fast as RAM? Much slower?
I tried to research on my own some, but it is difficult to tell from the specs. (E.g., SSDs don't have RPM ratings.)
Well, RPM wouldn't actually tell you how fast the drive is in the first place...you want to be looking at actual transfer rates, not what speed the drive spins at.
At any rate, SSDs are much faster with random read/write operations than mechanical hard drives, as there is virtually no seek time. Transfer rates on SSDs are not necessarily higher than HDD (depends on the price point and quality of the SSD), but that really only matters when doing operations on large files. For operating system use, zero seek time is going to give you a much larger practical benefit than higher transfer rates would.
But RAM is many many times faster than either SSD or HDD. There isn't even a comparison with current drive technology.
Intel SSD will provide some useful information for users;
Intel® High Performance SATA Solid-State Drives (SSDs) are designed to deliver outstanding performance and reliability. With no moving parts, Intel SSDs offer a quiet storage solution that responds quickly and uses less power. Compared to traditional hard disk drives, Intel SSDs are significantly more responsive, much more reliable, have lower power consumption and are completely quiet.
Intel SSDs are designed and validated specifically for PC applications using Intel's deep knowledge and understanding of PC design. Details include:
Use of high performance Open NAND Flash Interface (ONFI) working group spec flash chips
Parallel 10 channel architecture for high sustained read/write bandwidth
Extremely high random access speeds (I/O operations per second or IOPs) that are tuned for typical PC applications and modern operating systems
Typical user information & sales support information. Look at the technical specs & additional information on the Intel site.
RAMdisk do provide a means to have very fast storage or intermediate storage for web page presentations, data encryption or temp storage that will be dropped whenever power state is changed or reboots.
RAMdisk boards are not CHEAP! But very efficient when setup properly. The RAMdisk wiki will help define. Several advantages of using a RAMdisk, Instrumentation for data collection for high data rates or Medical Instrumentation for data analysis. Data storage latency for a RAMdisk will be dependent on the control circuits for the RAM. Most RAMdisk will have a battery or other means to keep the data valid when power is lost to the system.
If you do not wish to purchase a RAMdisk then you could look at Linux Ramdisk mini-HOWTO.
Dated but applicable, you will need to tweak things a bit but you can experiment to see the advantages.
The mix of storage systems can be an advantage when utilized by a knowledgeable user.
I But where do Solid-State Drives fit into this spectrum? Are they faster than mechanical hard-drives? Much faster? Are they as fast as RAM? Much slower?
Yes, yes (depending), no, quite a bit.
Note that even if you did have a simple figure that you could compare (rpm, seek time, peak bandwidth, sustained bandwidth or whatever else you could come up with) it wouldn't be a good comparison. SSDs are really quite fast in read, but not so fast in write, something that hard disks don't share, so whatever comparison you come up with would be quite heavily dependant on the exact data pattern. And hard disks are really quite slow in seek/latency, something that SSDs don't share, so again the exact results are going to depend heavily on the data patterns.
Actually head R/W actuator latency along with spindle rotation speed does play a roll when checking the drive performance. As the platter density increases then this factor does change to the advantage of accessing the data on the platter faster. One of the reasons to get a HDD with a larger cache.
Block data can be stored on a HDD then shared via the cache or RAMdisk for presentation.That's one of the advantages to use a SSD or invest in a separate RAMdisk to allow faster access to data R/W for a HDD.
Personally, I use SSD & SATA HDD that does mean a little more thought when partitioning on either.
The biggest advantage for SSD & RAMdisk are the lack of mechanical parts for access and the power usage thus longer battery life for mobile. Less power means less heat thus the use on desktops/laptops is a real plus for heat flow within the boxen. Look at the above links to enlighten about specs for SSD. Throw in access then you have a bigger plus. For HDD use Google to find loads of data or specs.