Received: from localhost (unknown [200.46.204.182]) by postgresql.org (Postfix) with ESMTP id 1C0DA9F96F7 for ; Wed, 12 Sep 2007 02:44:33 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.182]) (amavisd-maia, port 10024) with ESMTP id 36038-05 for ; Wed, 12 Sep 2007 02:44:28 -0300 (ADT) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.5 Received: from fk-out-0910.google.com (fk-out-0910.google.com [209.85.128.185]) by postgresql.org (Postfix) with ESMTP id 2CA4A9F96AD for ; Wed, 12 Sep 2007 02:44:29 -0300 (ADT) Received: by fk-out-0910.google.com with SMTP id b27so95423fka for ; Tue, 11 Sep 2007 22:44:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:references; bh=9AWp0/qltCpm9GTltJt+De31pg/mLALIwEqoX/yLoj0=; b=lhbCiZIPPghbhfUYwav0ZZXvAx/yhAn4Yg9aac0WBEolCsV09P3xnuyjUU1RVJEUlvSqgCcyPEqCSNjdN61w8Qpig1np7poNoFawvV4txHxdDkUV3lx/Bs/urNvoKiFXQuMZy57HWiCykY1cwCyz54t3DE7JsQ5qgk7gqo6fPLw= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:references; b=NKZzf11wQSiMeU4LBKcKmpRR1bCK+uTNbRjoJGbw+vnmpC2H+rlOrJ2KW6uy7aEYPFRQUFebmEBnMRxEYE2ko2EYK5NB7hoURzPZt6S5hsbP/JKp1ogD3BnPisH7VRex1uUWM5I6AWj+yQTpoYv4ooL5/oFgJJ+kh1Id6obg4nM= Received: by 10.82.178.11 with SMTP id a11mr2817144buf.1189575867724; Tue, 11 Sep 2007 22:44:27 -0700 (PDT) Received: by 10.82.105.9 with HTTP; Tue, 11 Sep 2007 22:44:27 -0700 (PDT) Message-ID: Date: Wed, 12 Sep 2007 11:14:27 +0530 From: "Harsh Azad" To: "david@lang.hm" Subject: Re: SAN vs Internal Disks Cc: Decibel! , pgsql-performance@postgresql.org In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_22363_32243730.1189575867720" References: <20070907100446.GE1795@mathom.us> <20070907103341.GC20896@oppetid.no> <20070911205550.GA38801@decibel.org> <20070911210857.GQ1795@mathom.us> <20070911230744.GJ38801@decibel.org> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200709/217 X-Sequence-Number: 26762 ------=_Part_22363_32243730.1189575867720 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Yeah, the DAS we are considering is Dell MD3000, it has redundant hot swappable raid controllers in active-active mode. Provision for hot spare hard-disk. And it can take upto 15 disks in 3U, you can attach two more MD1000 to it, giving a total of 45 disks in total. -- Harsh On 9/12/07, david@lang.hm wrote: > > On Tue, 11 Sep 2007, Decibel! wrote: > > > On Tue, Sep 11, 2007 at 05:09:00PM -0400, Michael Stone wrote: > >> On Tue, Sep 11, 2007 at 03:55:51PM -0500, Decibel! wrote: > >>> Also, to reply to someone else's email... there is one big reason to > use > >>> a SAN over direct storage: you can do HA that results in 0 data loss. > >>> Good SANs are engineered to be highly redundant, with multiple > >>> controllers, PSUs, etc, so that the odds of losing the SAN itself are > >>> very, very low. The same isn't true with DAS. > >> > >> You can get DAS arrays with multiple controllers, PSUs, etc. DAS != > >> single disk. > > > > It's still in the same chassis, though, which means if you lose memory > > or mobo you're still screwed. In a SAN setup for redundancy, there's > > very little in the way of a single point of failure; generally only the > > backplane, and because there's very little that's on there it's > > extremely rare for one to fail. > > not nessasarily. direct attached doesn't mean in the same chassis, > external drive shelves attached via SCSI are still DAS > > you can even have DAS attached to a pair of machines, with the second box > configured to mount the drives only if the first one dies. > > David Lang > > ---------------------------(end of broadcast)--------------------------- > TIP 2: Don't 'kill -9' the postmaster > -- Harsh Azad ======================= Harsh.Azad@gmail.com ------=_Part_22363_32243730.1189575867720 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline Yeah, the DAS we are considering is Dell MD3000, it has redundant hot swappable raid controllers in active-active mode. Provision for hot spare hard-disk. And it can take upto 15 disks in 3U, you can attach two more MD1000 to it, giving a total of 45 disks in total.

-- Harsh

On 9/12/07, david@lang.hm <david@lang.hm> wrote:
On Tue, 11 Sep 2007, Decibel! wrote:

> On Tue, Sep 11, 2007 at 05:09:00PM -0400, Michael Stone wrote:
>> On Tue, Sep 11, 2007 at 03:55:51PM -0500, Decibel! wrote:
>>> Also, to reply to someone else's email... there is one big reason to use
>>> a SAN over direct storage: you can do HA that results in 0 data loss.
>>> Good SANs are engineered to be highly redundant, with multiple
>>> controllers, PSUs, etc, so that the odds of losing the SAN itself are
>>> very, very low. The same isn't true with DAS.
>>
>> You can get DAS arrays with multiple controllers, PSUs, etc.  DAS !=
>> single disk.
>
> It's still in the same chassis, though, which means if you lose memory
> or mobo you're still screwed. In a SAN setup for redundancy, there's
> very little in the way of a single point of failure; generally only the
> backplane, and because there's very little that's on there it's
> extremely rare for one to fail.

not nessasarily. direct attached doesn't mean in the same chassis,
external drive shelves attached via SCSI are still DAS

you can even have DAS attached to a pair of machines, with the second box
configured to mount the drives only if the first one dies.

David Lang

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TIP 2: Don't 'kill -9' the postmaster



--
Harsh Azad
=======================
Harsh.Azad@gmail.com
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