# Can someone explain the different Crystaldiskmark tests?



## Blindsay

bump


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## Blindsay

anyone?


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## Blindsay

guess not?


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## Boyboyd

I'm going to take a stab at it, but i'm no expert so if anyone really knows please feel free to correct me.

*Sequential:* Crystal disk mark (CDM) reads/writes whatever file size you choose when you start the test sequentially. That is to say it starts writing on a sector and then writes the next part on the adjacent sector and so on. This is fastest because the head doesn't have to move about a lot as all the sectors are adjacent.

*512k*: CDM read/writes to *random* sectors on the drive, but it reads/writes 512KB of data at a random point, then moves to the next random point. This is faster than 4k because there's more data read/written with less movement of the head.

*4k*: The same as above but instead of reading/writing the test data in 512KB 'chunks' it reads/writes in 4KB chunks.

*4kQD32*: The same as 4K but there are more requests for the data sent to the HDD controller. I'm told that some HDDs increase performance when this happens because of the way their controller logic works but I think this mostly applies to SSDs not mechanical drives.

Fantastic image from wikipedia


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## Blindsay

Quote:


> Originally Posted by *Boyboyd*
> 
> I'm going to take a stab at it, but i'm no expert so if anyone really knows please feel free to correct me.
> *Sequential:* Crystal disk mark (CDM) reads/writes whatever file size you choose when you start the test sequentially. That is to say it starts writing on a sector and then writes the next part on the adjacent sector and so on. This is fastest because the head doesn't have to move about a lot as all the sectors are adjacent.
> *512k*: CDM read/writes to *random* sectors on the drive, but it reads/writes 512KB of data at a random point, then moves to the next random point. This is faster than 4k because there's more data read/written with less movement of the head.
> *4k*: The same as above but instead of reading/writing the test data in 512KB 'chunks' it reads/writes in 4KB chunks.
> *4kQD32*: The same as 4K but there are more requests for the data sent to the HDD controller. I'm told that some HDDs increase performance when this happens because of the way their controller logic works but I think this mostly applies to SSDs not mechanical drives.
> Fantastic image from wikipedia


cool, thats kinda what i thought but i wanted to make sure, thanks for the reply +rep


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## Kramy

CDM is more relevant to SSDs. 4K results are more synthetic on HDDs... they represent the bare minimum performance you'll see. 64K results would be more accurate for a drive's performance, because even tiny files like web browser cache are roughly that size. But 64K is _not_ part of the benchmark.

4K is quite interesting on SSDs, because it can vary so much between firmware versions or AHCI driver versions, which can reveal a lot about the efficiency of firmware/drivers/etc.

Sequential performance and 512K performance are both useful. If you crank up the test size you can find the whatever speed the drive can sustain, or if you lower it to ~50MB/100MB you can test how much cache helps performance when dealing with small amounts of data. Interesting.









I also like HDTune's graphs, since the slopes of the yellow dots and the blue arc can tell you a lot. For example, if you fill a drive almost entirely, data will be all over the place (including on the end), so you can see how much that impacts performance/responsiveness.










Some seeks on this WD Green take 40ms. That's nearly 3 frames in a game. Towards the end it drops to 50-75MB/sec. It's not suitable as a games drive.










This Hitachi's upper limit is around 25ms, and its sequential performance is higher. (75-90MB/sec towards the end) It's less likely to cause stutters and is more suitable for games.










This WD Black is most suitable. It has low access times and a high average speed. Access times climb gradually compared to the Hitachi (which has a steeper slope), so other software accessing this drive won't cause as big of stutters. It would definitely be the best choice as a games drive. (If it weren't already in use.







)


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## Blindsay

Quote:


> Originally Posted by *Kramy*
> 
> CDM is more relevant to SSDs. 4K results are more synthetic on HDDs... they represent the bare minimum performance you'll see. 64K results would be more accurate for a drive's performance, because even tiny files like web browser cache are roughly that size. But 64K is _not_ part of the benchmark.
> 4K is quite interesting on SSDs, because it can vary so much between firmware versions or AHCI driver versions, which can reveal a lot about the efficiency of firmware/drivers/etc.
> Sequential performance and 512K performance are both useful. If you crank up the test size you can find the whatever speed the drive can sustain, or if you lower it to ~50MB/100MB you can test how much cache helps performance when dealing with small amounts of data. Interesting.
> 
> 
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> 
> I also like HDTune's graphs, since the slopes of the yellow dots and the blue arc can tell you a lot. For example, if you fill a drive almost entirely, data will be all over the place (including on the end), so you can see how much that impacts performance/responsiveness.
> 
> 
> 
> 
> 
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> 
> Some seeks on this WD Green take 40ms. That's nearly 3 frames in a game. Towards the end it drops to 50-75MB/sec. It's not suitable as a games drive.
> 
> 
> 
> 
> 
> 
> 
> 
> This Hitachi's upper limit is around 25ms, and its sequential performance is higher. (75-90MB/sec towards the end) It's less likely to cause stutters and is more suitable for games.
> 
> 
> 
> 
> 
> 
> 
> 
> This WD Black is most suitable. It has low access times and a high average speed. Access times climb gradually compared to the Hitachi (which has a steeper slope), so other software accessing this drive won't cause as big of stutters. It would definitely be the best choice as a games drive. (If it weren't already in use.
> 
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> 
> )


Thanks for the follow up, do SSD's do so well in the 4k because of their seek time (or rather lack of) and then in turn thats what makes them feel so snappy? because with sequential numbers they are mechanical drives that match SATA2 SSD's


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## Kramy

Quote:


> Originally Posted by *Blindsay*
> 
> Thanks for the follow up, do SSD's do so well in the 4k because of their seek time (or rather lack of) and then in turn thats what makes them feel so snappy? because with sequential numbers they are mechanical drives that match SATA2 SSD's


That's exactly it.

Most HDDs have (at the minimum) somewhere around 10ms seek times, capping them to doing about 100 things per second. Sequentially, it's all good - seek once (10ms) and read sequentially for however long. But as soon as a drive must multitask, much of its time gets burned up seeking back and forth. 4K IOPS reveals how well a drive does when under heavy multitasking loads.


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