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Home > Archive > Data Storage > March 2005 > Raid 0+1 vs raid 5 with 4 hard drives
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Raid 0+1 vs raid 5 with 4 hard drives
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| Hi,
I'm building a new system with 4 hard drives and i have to chose
between a raid 0+1 or a raid 5 setup. This is for home use which means
i don't care if the system goes down in the case of a hard drive
failure but i want at least minimal data security so i ruled out raid
0. I'd say that performance is the biggest issue but i am ready to
make some tradeoff for the extra storage capacity raid 5 offers if
there is only a minor difference. Also, price is not an issue. I'd
really appreciate it if you could provide me with some theorical
statistics on the read/write/access time speed for a raid 5 setup (i
know this may depends on the quality of the controller).
For example:
Raid 0+1 (4 disk)
Storage capacity: 200%
Read: ~400% (not entirely true but for the sake of simplicity)
Write: 200%
Access: ?
Raid 4 (4 disk)
Storage capacity: ~300%
Read: ?
Write: ?
Access: ?
Thanks and sorry for my bad english
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| up3000@gmail.com 2005-03-28, 8:46 pm |
| if write operation > 20% , raid 0+1 is a better choice
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| Bill Todd 2005-03-29, 2:46 am |
| bps wrote:
....
I'd say that performance is the biggest issue but i am ready to
> make some tradeoff for the extra storage capacity raid 5 offers if
> there is only a minor difference
As usual, the answer is "It depends..."
First, it depends upon the intelligence in the RAID software or firmware
you use: if it's pretty dumb, then it won't get all the performance
that it could.
But if it's optimal, then read operations should be about equal in
performance regardless of whether you use RAID-1 or RAID-5: all the
disks can potentially satisfy independent parallel read requests, or
could satisfy streaming reads at their combined bandwidth.
Writes are more variable. In the worst case (small random writes)
RAID-5 can take as much as twice as long to complete each write (halving
potential throughput, since the operation ties up 2 disks with either
approach), whereas in the best case (streaming writes) a 4-disk RAID-5
configuration could actually offer about 50% more write bandwidth than a
4-disk RAID-1 configuration.
- bill
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| Faeandar 2005-03-29, 2:46 am |
| On 28 Mar 2005 17:44:32 -0800, arak123@email.com (bps) wrote:
>Hi,
>
>I'm building a new system with 4 hard drives and i have to chose
>between a raid 0+1 or a raid 5 setup. This is for home use which means
>i don't care if the system goes down in the case of a hard drive
>failure but i want at least minimal data security so i ruled out raid
>0. I'd say that performance is the biggest issue but i am ready to
>make some tradeoff for the extra storage capacity raid 5 offers if
>there is only a minor difference. Also, price is not an issue. I'd
>really appreciate it if you could provide me with some theorical
>statistics on the read/write/access time speed for a raid 5 setup (i
>know this may depends on the quality of the controller).
>
>For example:
>
>Raid 0+1 (4 disk)
> Storage capacity: 200%
> Read: ~400% (not entirely true but for the sake of simplicity)
> Write: 200%
> Access: ?
>
>Raid 4 (4 disk)
> Storage capacity: ~300%
> Read: ?
> Write: ?
> Access: ?
>
>Thanks and sorry for my bad english
I think up3000 sum'd it up nicely. That's a decent rule of thumb for
uses like what you describe.
The thing about controller quality is a slippery fish. Most of the
home-based controllers have issues when it comes to performance,
probably because that's not usually top on the home user list.
I've heard of some controllers still using system cpu to calculate
parity, in which case raid5 will kill you.
All things being equal, and if price is not an issue for you, I'd go
with raid0+1. And if you need more space get 2 controllers, 8 drives,
and use a volume manager to concatenate them together.
~F
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