[Question] Slow write speeds with Raid 6

[Casia]

Hi

Until a few days I've this configuration

- Adaptec 5805 + 8 WD20EARS in JBOD
- 3Ware 9690SA-8I + 8 WD20EARS in JBOD

I've good read/write times and no problems. Last week I changed my mobo to an ASRock Z68 Extreme4 Gen 3 with no BIOS and Adaptec card stops working

I've a Chenbro SAS Expander (CK12804) so I used it with the 3ware

Now I've:

- 3Ware 9690SA-8I -> Chenbro CK12804 -> 16 WD20EARS

But I've a lot of problems:

- In Raid 6 (hardware) get write speeds very lows (around 20mbs) (after he completes the "Initializing")
- Creating a single disk with LVM get good speeds during the first hour, after that it starts to write very slowly (around 30mbs)

Where is the problem? 3Ware works fine with the other configuration, maybe the Chenbro is working bad?
Or maybe I'm doing something wrong making the Raid?

Regards (and sorry for my poor english)

 

[drescherjm]

Do you have a BBU installed?
Are you using write back cache?

 

[Casia]

No BBU
In the administration utility on the 3Ware when make the raid I choose "Write Cache: Intelligent" (is de default option) but don't find anything about write back cache

Regards

 

[MrGuvernment]

update firmware on the drives?

raid 6 can be slow since it has to do double the parity that raid 5 does.

the adaptec card, just nothing happens? wont boot?

try another pcie slot?

 

[Casia]

Adaptec don't support boot in UEFI motherboards: http://ask.adaptec.com/scripts/adap...td_adp.php?p_faqid=17087&p_created=1305289854

I updated the firmware on the 3ware before make the raid, discs are new ones (not the olds used in the other jbods) but I'll try to update the firmwares tomorrow

 

[drescherjm]

No BBU
In the administration utility on the 3Ware when make the raid I choose "Write Cache: Intelligent" (is de default option) but don't find anything about write back cache

Regards

Intelligent probably means write through without a BBU.

 

[MrGuvernment]

Adaptec those sneaky mother fudders.....how could they not..

 

[Casia]

BBU gives me better speeds? I'm looking for it on ebay and prices are around 100€, not expensive