freebsd-performance Digest, Vol 4, Issue 7

[Petri Helenius]

> agent dero wrote:
>
> > I have been researching RAID and Software RAID online using FreeBSD's
> > availible documents, and I am wondering what the performance of using a
> > simple RAID 1 capable card over a software RAID 1 configuration? Will the
> > software RAID perform well enough that I could just cut costs of a RAID card?
> >

For mirroring (RAID 1) or mirroring + striping (RAID10 or RAID0+1) the hardware
on a RAID card does not really give you a much, just saves you one DMA from
the main memory for the other write on the redundant disk. And depending on
driver and if you purchased the battery backup on the card, might give you benefits
from write ordering.

>
> Recently, we tested software RAID via CCD and VINUM, and compared
> them to adaptec 2xxx RAID controller. The performance is the same.
> The CPU are Xeon 2.8 GHz, SuperMicro MB with ServerWork Chipset.
> Seagate 3147xxxxLC drives.
>
> Problem is the write is slow for all of them, especially when multiple writes.
>
Write shouldn´t be too slow on RAID1. On RAID5 it depends on the implementation,
how much overlapping it does and how much overlapping does your test have.

> Heard from Adaptect that their 5400 RAID has best performance, but
> never had one for testing.
>
If I understand correctly it has been discontinued.

> So, soft RAID is ok to save bucks for hardware.
>
And currently there are also the reliability issues with drivers like aac
(Adaptec 2120S and 2200S, etc.) "no frills" SCSI or ATA controllers
run much more reliably and have more user base so the issues get ironed
out quicker.

Pete