Re: Promise RAID-1 vs software RAID-1
From: Christopher Chan (cchan_at_outblaze.com)
Date: 06/17/04
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Date: Thu, 17 Jun 2004 07:22:06 +0800 To: For users of Fedora Core releases <fedora-list@redhat.com>
Rodolfo J. Paiz wrote:
> At 10:39 6/16/2004, Alan Horn wrote:
>
>> Raid 1 is mirroring only. For data integrity reasons I can't see how
>> they could read from any but the master mirror.
>
>
> WAG alert:
>
> Once the two disks are synchronized, it sounds perfectly reasonable to
> writes to take the same amount of time (since all data has to be written
> to both drives), but for reads to be significantly faster by reading
> from both spindles. There really is no "master" in an equal set of two,
> I think. Both contain identical data, so you should be able to read from
> both. I think.
The Linux kernel does give you the ability to read simultaneously from
both drives in a Linux mirror array.
>
> By the way, the Promise cards *are* software RAID... all the real RAID
> computations are done by the driver using the computer's resources. The
> trick is that the binary driver for Linux is probably less mature and
> less flexible than Linux native software RAID, so I've always used
> Promise and HighPoint controllers simply as additional EIDE/ATA
> controllers and used Linux software RAID. Excellent results. Note that
> Linux software RAID is also capable of RAID-5, IIRC, which the Promise
> drivers are not.
Heh, exactly the same reason here. Any Promise installation we had was
for ATA100 support.
>
> If you have the budget, I'd strongly recommend the 3Ware cards. Real
> hardware RAID, native Linux kernel support since 2.2.x, fast, very
> reliable, and not expensive.
Some gotchas:
3ware RAID 5 sucks and especially when in degraded mode (and this goes
for a lot of other hardware RAID cards) because the onboard processor is
not fast enough to handle the calculations. Hint: If you see an Intel
960 processor on your RAID board, forget RAID 5.
Linux RAID 5 will be much faster so forget the 3ware RAID card if you
want to do RAID 5.
3ware RAID 1+0 also sucks. You are better off configuring two mirrors
and using the Linux kernel to achieve the RAID 0 part. This means that,
depending on what you got (4 port/8 port/12 port), you will need other
disks on the IDE channels for the system if there is nothing left for
the system.
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- Previous message: Erik Espinoza: "Re: FC2 & Nivdia Drivers"
- In reply to: Rodolfo J. Paiz: "Re: Promise RAID-1 vs software RAID-1"
- Next in thread: Christopher Chan: "Re: Promise RAID-1 vs software RAID-1"
- Reply: Christopher Chan: "Re: Promise RAID-1 vs software RAID-1"
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