Re: Table locking problems?

От: Dan Harris
Тема: Re: Table locking problems?
Дата: ,
Msg-id: 17797211-4C5F-4410-B38E-53ECC10D0752@drivefaster.net
(см: обсуждение, исходный текст)
Ответ на: Re: Table locking problems?  (John A Meinel)
Ответы: Re: Table locking problems?  (John A Meinel)
Список: pgsql-performance

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Table locking problems?  (Dan Harris, )
 Re: Table locking problems?  ("Joshua D. Drake", )
  Re: Table locking problems?  (Tom Lane, )
   Re: Table locking problems?  (Dan Harris, )
 Re: Table locking problems?  (Michael Fuhr, )
 Re: Table locking problems?  (Steve Poe, )
  Re: Table locking problems?  (Dan Harris, )
   Re: Table locking problems?  (John A Meinel, )
    Re: Table locking problems?  (Dan Harris, )
     Re: Table locking problems?  (John A Meinel, )

On Aug 9, 2005, at 3:51 PM, John A Meinel wrote:

> Dan Harris wrote:
>
>> On Aug 10, 2005, at 12:49 AM, Steve Poe wrote:
>>
>>> Dan,
>>>
>>> Do you mean you did RAID 1 + 0 (RAID 10) or RAID 0 + 1? Just a
>>> clarification, since RAID 0 is still a single-point of failure
>>> even if
>>> RAID1 is on top of RAID0.
>>>
>> Well, you tell me if I stated incorrectly.  There are two raid
>> enclosures with 7 drives in each.  Each is on its own bus on a
>> dual- channel controller.  Each box has a stripe across its drives
>> and the  enclosures are mirrors of each other.  I understand the
>> controller  could be a single point of failure, but I'm not sure I
>> understand  your concern about the RAID structure itself.
>>
>
> In this configuration, if you have a drive fail on both
> controllers, the entire RAID dies. Lets label them A1-7, B1-7,
> because you stripe within a set, if a single one of A dies, and a
> single one of B dies, you have lost your entire mirror.
>
> The correct way of doing it, is to have A1 be a mirror of B1, and
> then stripe above that. Since you are using 2 7-disk enclosures,
> I'm not sure how you can do it well, since it is not an even number
> of disks. Though if you are using software RAID, there should be no
> problem.
>
> The difference is that in this scenario, *all* of the A drives can
> die, and you haven't lost any data. The only thing you can't lose
> is a matched pair (eg losing both A1 and B1 will cause complete
> data loss)
>
> I believe the correct notation for this last form is RAID 1 + 0
> (RAID10) since you have a set of RAID1 drives, with a RAID0 on-top
> of them.
>

I have read up on the difference now. I don't understand why it's a
"single point of failure".  Technically any array could be a "single
point" depending on your level of abstraction.   In retrospect, I
probably should have gone 8 drives in each and used RAID 10 instead
for the better fault-tolerance,  but it's online now and will require
some planning to see if I want to reconfigure that in the future.  I
wish HP's engineer would have promoted that method instead of 0+1..

-Dan



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