Re: mdadm - two questions
On Nov 30, 2016, at 3:40 AM, Kamil Jońca <kjonca@poczta.onet.pl> wrote:
> Rick Thomas <rbthomas@pobox.com> writes:
>
>> Hi Kamil,
>>
>> You’d get a bit more space by configuring your 4 drives as a RAID5
>> array (3TB usable for RAID5, vs 2TB usable for RAID10). The downside
>> of RAID5 is that the RAID10 (or the one LV with two RAID1 PVs — they
>> amount to the same thing for this discussion) can survive loosing two
>> drives at once — if they happen to be the right two drives: i.e. not
>> both sides of a single mirrored pair — while RAID5 would not be able
>> to survive any failure that involved two drives at once. Either
>> configuration would survive loosing any one single drive, of course.
>>
>> If you want to be able to survive simultaneous loss of any two drives, you should look at RAID6, which would have the same usable capacity (2TB) as the RAID10.
>
> I though about this, but I'm afraid about performance (calculating
> control sums ). Needlessly?
> KJ
There’s a three-way tradeoff: usable space; performance; survivability.
For my application (backups), performance is less important than space and survivability. The performance hit definitely exists, but I do not find it a problem. Of course, YMMV — “your milage may vary".
Enjoy!
Rick
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