[Box Backup] userland RAID 5 vs RAID 1 consideration

[Ben Summers]

On 21 Sep 2004, at 22:27, Garry Glendown wrote:

> Tomasz Nowak wrote:
>> 1. Storage performance is rather not the case on backup
>>    machine; RAID 1 would perfectly do the job.
>> 2. Reliability of RAID 1 is just the same as RAID 5.
>> 3. Each RAID 1 array is 33% cheaper then RAID 5 array.
>
> It is? 250G of RAID1 storage cost you 500G of raw storage, whereas 
> 250G of RAID5 is only 375G of raw storage ... or other way around, two 
> 250G HDs give you a total of 250G RAID1, three 250G HDs give you 500G 
> of RAID5 ... for performance, I/O might be slightly better for RAID5, 
> though CPU load is probably slightly higher ...

Garry is correct. RAID5 gives you 66% of the hard discs as usable 
space, RAID1 only 50%. However, prices of hard discs may make RAID1 
have a cheaper per-Gb cost than RAID5.

With Box Backup's implementation of RAID, performance would be the 
same. (Turning files into their RAID representation is delayed until 
after all the data is written.)

Of course, you can choose whatever RAID level you want by putting Box 
Backup into non-RAID mode and using the underlying OS to do it instead.

Ben