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On 30/09/11 14:20, Tim Connors wrote:
> On Fri, 30 Sep 2011, Adam Goryachev wrote:
>
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>> On 30/09/11 04:11, Mike Dresser wrote:
>>> Just finishing up moving one of my backuppc servers to new larger disks,
>>> and figured I'd submit a success story with backuppc_tarpccopy... I
>>> wanted to create a new xfs filesystem rather than my usual dd and
>>> xfsgrowfs, as this thing has been in use since backuppc 2.1 or similar.
>>> Old disks were 10 x 1TB in raid10, new is 6 x 3TB's in raid6 (which in
>>> itself has been upgraded many times).. the new raid6 is FAR faster in
>>> both iops and STR than the old one.
>>
>> Hi,
>>
>> I'm curious that you say you are getting better performance from the new
>> RAID6 compared to the old RAID10.
>>
>> Can I assume this is because the new HDD's perform better than the old?
>> In other words, would it be safe to assume you would get even better
>> performance using RAID10 with the new HDD's than you are getting with RAID6?
>>
>> I'm just curious, I'm fairly confident that RAID10 always performs
>> better than RAID5 or RAID6. Just want to make sure I'm not making a mess
>> of things by using RAID10 over RAID6.
>>
>> Can anyone suggest any advantage of RAID6 over RAID10 (aside from the
>> obvious additional storage capacity/reduced wastage of space)?
>
> Worst case, if you lose one disk, then rebuild, and during rebuild,
> suffer the likely consequence of losing another disk when rebuilding
> raid6, you still have a valid array.
>
> Worse case, fairly likely occurence with raid10, lose that second disk and
> lose all your data.
Ummm, considering RAID10 with 10 disks, if you lose one disk, and lose a
second disk, you are unlikely to have lost all your data (but possibly,
about 1/9 I think). In fact, it would be possible to lose 5 disks
without losing your data, though you would be very unlucky to lose 5
disks, and very lucky to lose the "right" 5...
> Care for your data ==> don't use raid10.
So if I'm right, the advantage of RAID6 over RAID10 is that you can lose
any two disks without data loss.
The advantage of RAID10 over RAID6 is performance and that if you are
lucky you can lose up to half your disks without data loss.
Regards,
Adam
- --
Adam Goryachev
Website Managers
www.websitemanagers.com.au
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