# RAID 5 array with SSD cache



## $immond$ (Jul 21, 2011)

Alright so I am interested in setting a RAID 5 array and using an SSD as cashe. 

Adaptec RAID 6405 2270000-R 6Gb/s SATA/SAS 4 inter...

I am interested in the Adaptec RAID 6405 2270000-R but I dont know if my hard drives are compatible, I cant find it on there list.

http://download.adaptec.com/pdfs/compatibility_report/arc-sas_cr_07-01-11_series6e_lowport.pdf 

I have 2 WD Blacks (WD6402AAEX) and I will get a 3rd one if its supported. 

Anyone have experience with this card? Does anyone know if the WD blacks work well with it? Also what size of SSD should I use for the cashe? Is there a particular ratio depending on the size of the raid array? :S


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## $immond$ (Jul 21, 2011)

If not can anyone recommend some decent performing disks or a compatible RAID card. It would be greatly appreciated.


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## newtekie1 (Jul 21, 2011)

I'm not sure about the WD Black drives and that Controller, that might be something you have to ask Adaptec directly.  I know the WD Black drives can have issues with certain controllers though, especially if they are the new versions that completely remove TLER.

As for the size of the SSD cache, I don't believe anything over 64GB would give any improvement.  So stick with 64GB or less, IMO.


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## Disparia (Jul 21, 2011)

I don't believe that controller has the support you're looking for - Adaptec calls it MaxCache and there are only three controllers with it at this time. They're also limited to Intel SSD as cache. The 6405 does support Hybrid RAID, for levels 1 and 10. Writes to both, reads from only the SSD(s).

LSI has CacheCade, which is more versatile than MaxCache, but it's a $270 add-on last time I checked, on top of the cost of the controller.

The Z68 chipset can set an SSD to cache an entire array, but that would require a new board/cpu.

The rest of the solutions that I know of (Highpoint... and I'm drawing a blank on the other two) involve having one SSD and one HDD. Your 120GB could cache a single 640GB, with the other 640GB as a backup drive. Might not be as ideal as the other solutions, but is very cheap.


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## $immond$ (Jul 21, 2011)

Jizzler said:


> I don't believe that controller doesn't have the support you're looking for - Adaptec calls it MaxCache and there are only three controllers with it at this time. They're also limited to Intel SSD as cache. The 6405 does support Hybrid RAID, for levels 1 and 10. Writes to both, reads from only the SSD(s).
> 
> LSI has CacheCade, which is more versatile than MaxCache, but it's a $270 add-on last time I checked, on top of the cost of the controller.
> 
> ...



RAID Support
 The Adaptec RAID 6405 controller card supports multi-level RAID configuration including RAID 0, 1, 1E, 5, 5EE, 6, 10, 50, 60, JBOD for better performance, enhanced data security and flexible capacity upgrades. It also *support HDD+SSD hybrid RAID *for further enhanced performance. (Expander is necessary for Level 50, 60.)

I guess my only option is to email the company and find out if my drives are supported or try to find some drives on the compatibilty chart that will work.


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## Disparia (Jul 21, 2011)

Yup. And they define Hybrid RAID support here: http://www.adaptec.com/en-us/_common/hybrid-raid/



> The controller takes care of the rest by automatically creating a Hybrid RAID array whenever you use one or more SSDs and combine them with the same number of HDDs to create a RAID 1 or RAID 10 array.



Looks like they want you to spend more to get the RAID-5 support (MaxCache controllers are pricey). And not just RAID-5 support, but caching support in general. This is in their knowledgebase:



> Question: Can any capacity of Solid State and hard disk drives be used to create a Hybrid RAID?
> Answer: Yes. If the RAID array is built from different-sized drives, the drive segment size is the size of the smaller disk drive.
> Example: A RAID 1 created with one 64GB SSD and one 1TB HDD will make a 64GB logical device. A RAID 10 created with two 128GB SSDs and two 1TB HDDs will make a 256GB logical device. Please note that for a Hybrid RAID10 an equal number of SSDs and HDDs has to used.


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## $immond$ (Jul 21, 2011)

So is there a certain ratio of GB for SSD to HDD needed for cashing with RAID 5? Am I missing a mathematical equation here??


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## Hotobu (Jul 23, 2011)

I'm not so sure SSD cache + RAID is a good idea. Not that it wont work, but part of the purpose of a RAID array is to combine the performance of all of the drives together. The bigger the RAID array the less of a benefit the cache becomes. RAID 5 read speed is ~ the sum of the speeds of all of the drives and RAID5 write speed ~ speed of all of the drives - 1 (also minus some performance for having to write parity info. 

The point is that if the RAID array is for storage, and you're not going to use it for a lot of simultaneous read/write operations using an SSD as cache isn't money well spent. You'd be much better off to just put your OS on the SSD, and run everything off of a RAID 5 array of 4 disks.

Someone feel free to correct me on this though.


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## Jetster (Jul 23, 2011)

Subscribed


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