| From: | Hannu Krosing <hannu(at)2ndQuadrant(dot)com> |
|---|---|
| To: | MauMau <maumau307(at)gmail(dot)com>, Hannu Krosing <hannu(at)2ndQuadrant(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kevin Grittner <kgrittn(at)ymail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Simon Riggs <simon(at)2ndQuadrant(dot)com>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Standalone synchronous master |
| Date: | 2014-01-09 15:55:22 |
| Message-ID: | 52CEC66A.1060204@2ndQuadrant.com |
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| Lists: | pgsql-hackers |
On 01/09/2014 04:15 PM, MauMau wrote:
> From: "Hannu Krosing" <hannu(at)2ndQuadrant(dot)com>
>> On 01/09/2014 01:57 PM, MauMau wrote:
>>> Let me ask a (probably) stupid question. How is the sync rep
>>> different from RAID-1?
>>>
>>> When I first saw sync rep, I expected that it would provide the same
>>> guarantees as RAID-1 in terms of durability (data is always mirrored
>>> on two servers) and availability (if one server goes down, another
>>> server continues full service).
>> What you describe is most like A-sync rep.
>>
>> Sync rep makes sure that data is always replicated before confirming to
>> writer.
>
> Really? RAID-1 is a-sync?
Not exactly, as there is no "master" just controller writing to two
equal disks.
But having a "degraded" mode makes it
more like async - it continues even with single disk and syncs later if
and when the 2nd disk comes back.
Cheers
--
Hannu Krosing
PostgreSQL Consultant
Performance, Scalability and High Availability
2ndQuadrant Nordic OÜ
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