Re: best base / worst case RAID 5,6 write speeds

[Alexander Afonyashin <a.afonyashin@madnet-team.ru>]

Hi,

Did you set stride/stripe configuration to filesystem that is aligned
with raid configuration?

Regards,
Alexander

On Thu, Dec 10, 2015 at 4:34 AM, Dallas Clement
<dallas.a.clement@gmail.com> wrote:
> Hi all.  I'm trying to determine best and worst case expected
> sequential write speeds for Linux software RAID with spinning disks.
>
> I have been assuming on the following:
>
> Best case RAID 6 sequential write speed is (N-2) * X, where is is
> number of drives and X is write speed of a single drive.
>
> Worst case RAID 6 sequential write speed is (N-2) * X / 2.
>
> Best case RAID 5 sequential write speed is (N-1) * X.
>
> Worst case RAID 5 sequential write speed is (N-1) * X / 2.
>
> Could someone please confirm whether these formulas are accurate or not?
>
>
> I am not even getting worst case write performance with an array of 12
> spinning 7200 RPM SATA disks.  Thus I  suspect either the formulas I
> am using are wrong or I have alignment issues or something.  My chunk
> size is 128 KB at the moment.
>
> Thanks,
>
> Dallas
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