Re: RAID 0+1 sofware or dedicated adapter for 7025 F50?

• Previous message: Collin McClendon: "Re: XDM and headless 7025-F50"
• In reply to: Steve Greatbanks: "Re: RAID 0+1 sofware or dedicated adapter for 7025 F50?"
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Date: Sun, 05 Oct 2003 13:12:22 -0400

This is what I was expecting...I have hardware RAID on my dual AMD
workstation at home and its very fast. However for our purposes since we
split a mirrored vg and back up the split and then delete the split and
mirror the vg again after, wouldn't we have to got with raid 0 in
hardware and the mirroring in software (LVM)? The reason I was told that
we had to do this is that we use cpio for backing up and our database
must be offline during a backup. We split off copies when the database
is offline and then put it back up on the live copy after the split. I
would hope there could be a way to back up this database (Sybase
licensed I believe) without going through this mirror splitting process.
Thanks for the suggestions and information,
Colin

Steve Greatbanks wrote:

> "Bill" <bverzal@komatsuna.com> wrote in message
> news:51157c68.0310031250.422a0fdc@posting.google.com...
>
>>Collin McClendon <cbmcclendon3aat@netscapedot.net> wrote in message
>
> news:<blk2h3$1tj$1@murdoch.acc.Virginia.EDU>...
>
>>>Hello all,
>>>My company is currently looking at boosting our performance on our main
>>>data processing server, a 4 way 7025-F50 (just went from 1 way to 4 way
>>>last week). We use Unidata which from what I have read uses much random
>>>I/O. I am thinking of buying 6 more disks which are faster than the 7200
>>>RPM ones (10K) and either using LVM to do RAID 0+1 or get two RAID
>>>adapters for a duplex 0+1 RAID setup. with 4 processors will my overhead
>>>for RAID 0+1 be too much? Will I get a huge increase in performance with
>>>a dedicated RAID adapter with this config? (Basically two 3 disk
>>>stripes mirrored across two non raid LVD controllers vs the two 3 disk
>>>stripes created via hardware RAID and mirrored using LVM (we have to
>>>split mirrors every day so we can backup our data)
>>>Thanks for any advice,
>>>Collin
>>
>>Hardware RAID is far faster than LVM RAID. RAID 10 (or 0+1) is
>>fastest for writes. Raid 5 is fastest for reads.
>
>
> Misinformation. A read from a RAID10 device should be faster than a read
> from a RAID5 device for the obvious reason that the RAID5 has a disk worth
> of distributed parity information compared to the RAID10.
> In short, the only advantage RAID5 has over RAID10 is you get more usable
> disk space from a given set of disks. You lose out in both read and write
> speed.
>
> In response to the original poster's question, the LVM mirroring (and more
> particularly the mirror write consistency) will slow you down in either
> situation. I agree that the hardware option would probably be somewhat
> quicker (especially if the RAID controllers have a decent cache on them),
> but you will be constrained by the LVM waiting for both writes to complete.
> If you have the money, go with the hardware RAID.
>
>

• Previous message: Collin McClendon: "Re: XDM and headless 7025-F50"
• In reply to: Steve Greatbanks: "Re: RAID 0+1 sofware or dedicated adapter for 7025 F50?"
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