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Pegasus R6, only use 4 drive raid

O

ogs

macrumors member
Original poster
Hey guys,

Just wondering if it's possible to use 4 of the 6 drives in the enclosure in a raid 5 setup, and then two other ones working independently too?

So on my computer I'd see:
Drive 1
Drive 2
Drive 3 (4 drive raid)
 
ogs said:
Could do raid 6, no write hole.
Click to expand...

RAID 6 doesn't get rid of the write hole problem. If anything it makes it worse since there is even more data to write to several different platters to complete the write operation transaction.
 
Last edited:
Hmmm then which method would be best for 4 drives in an array for safe storage
 
ogs said:
Hey guys,

Just wondering if it's possible to use 4 of the 6 drives in the enclosure in a raid 5 setup, and then two other ones working independently too?

So on my computer I'd see:
Drive 1
Drive 2
Drive 3 (4 drive raid)
Click to expand...

The user manual can be downloaded.


http://www.promise.com/support/down...SeriesSn=47&ModelSn=118&m=93&region=en-global

Around Page 55 is "Creating Disk Array and Logical Drive with the Wizard".

You probably want Express or Manual option. On express, 3 logical drives. one with redundancy+capacity+speed with no spare (should get you RAID 5) and two more logical drives with no redundancy, max capacity , no speed , and no spare . Or just manually spell all that out.
 
ogs said:
Hey guys,

Just wondering if it's possible to use 4 of the 6 drives in the enclosure in a raid 5 setup, and then two other ones working independently too?

So on my computer I'd see:
Drive 1
Drive 2
Drive 3 (4 drive raid)
Click to expand...
Yes, this is possible.

Any particular reason for focusing on the Promise Pegasus products?

I ask, as it's reliability isn't really known (Promise in general does well, but this product isn't very common in the field yet), and other solutions may be a better fit (i.e more flexible/better tailored to fit your specific needs).

You'd need to sit down and figure out what you actually need, and consider the answers to such questions as the following:
  • How much capacity do you need?
  • What sort of throughput do you need?
  • How much redundancy do you need?
  • What kind of backup system are you planning to run (keep in mind, RAID is not a substitute for a proper backup solution)?
  • What about future expansion?
  • Budget?

ogs said:
Could do raid 6, no write hole.
Click to expand...
As previously mentioned, RAID 6 does not eliminate the write hole issue (write hole issue exists in any traditional parity RAID level).

That said, there is a solution, but it's hardware based, which is why you need a proper RAID controller to deal with it (software based implementations of traditional parity levels cannot handle this issue at all).

Another thing to consider is a good UPS system.
 
ogs said:
Hmmm then which method would be best for 4 drives in an array for safe storage
Click to expand...

If safety is absolutely the very top priority then ... RAID 6 is slightly better.

Both can survive if the right two disks fail at the same time. In RAID-10 if both mirrors of one of the stripes fail you are lost. If the failure only occurs once in all the stripes (two in this case) then you are OK.

In RAID-6 the parity and data is spread out a bit more between the disks.


So a RAID-6 with the Mac and drive hooked to a battery back-up which would trigger a shutdown if switch to battery power for more than a minute or so. If that blows the budget then RAID-10 isn't bad. Keeping just the drive powered up with battery back-up is OK if know can get power back on before the battery runs out. That's not always possible in small shops or even big ones ( data centers near World Trade Center were without people and power for over a day and disk systems with batteries crapped out anyway. )


Both are about the same usable capacity. You get the capacity of two of the four disks used.
 
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