Date: Tue, 7 Jul 2015 12:28:18 +0200 (CEST)
From: "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>
To: "Graeme B. Bell" <graeme.bell@nibio.no>
Cc: Steve Crawford <scrawford@pinpointresearch.com>,
 "Wes Vaske (wvaske)" <wvaske@micron.com>,
 pgsql-performance <pgsql-performance@postgresql.org>
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Subject: Re: New server: SSD/RAID recommendations?
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Thread-Topic: [PERFORM] New server: SSD/RAID recommendations?
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Thanks for the Info.

So if RAID controllers are not an option, what one should use to build
big databases? LVM with xfs? BtrFs? Zfs?

Tigran.

----- Original Message -----
> From: "Graeme B. Bell" <graeme.bell@nibio.no>
> To: "Steve Crawford" <scrawford@pinpointresearch.com>
> Cc: "Wes Vaske (wvaske)" <wvaske@micron.com>, "pgsql-performance" <pgsql-performance@postgresql.org>
> Sent: Tuesday, July 7, 2015 12:22:00 PM
> Subject: Re: [PERFORM] New server: SSD/RAID recommendations?

> Completely agree with Steve.
> 
> 1. Intel NVMe looks like the best bet if you have modern enough hardware for
> NVMe. Otherwise e.g. S3700 mentioned elsewhere.
> 
> 2. RAID controllers.
> 
> We have e.g. 10-12 of these here and e.g. 25-30 SSDs, among various machines.
> This might give people idea about where the risk lies in the path from disk to
> CPU.
> 
> We've had 2 RAID card failures in the last 12 months that nuked the array with
> days of downtime, and 2 problems with batteries suddenly becoming useless or
> suddenly reporting wildly varying temperatures/overheating. There may have been
> other RAID problems I don't know about.
> 
> Our IT dept were replacing Seagate HDDs last year at a rate of 2-3 per week (I
> guess they have 100-200 disks?). We also have about 25-30 Hitachi/HGST HDDs.
> 
> So by my estimates:
> 30% annual problem rate with RAID controllers
> 30-50% failure rate with Seagate HDDs (backblaze saw similar results)
> 0% failure rate with HGST HDDs.
> 0% failure in our SSDs.   (to be fair, our one samsung SSD apparently has a bug
> in TRIM under linux, which I'll need to investigate to see if we have been
> affected by).
> 
> also, RAID controllers aren't free - not just the money but also the management
> of them (ever tried writing a complex install script that interacts work with
> MegaCLI? It can be done but it's not much fun.). Just take a look at the
> MegaCLI manual and ask yourself... is this even worth it (if you have a good
> MTBF on an enterprise SSD).
> 
> RAID was meant to be about ensuring availability of data. I have trouble
> believing that these days....
> 
> Graeme Bell
> 
> 
> On 06 Jul 2015, at 18:56, Steve Crawford <scrawford@pinpointresearch.com> wrote:
> 
>> 
>> 2. We don't typically have redundant electronic components in our servers. Sure,
>> we have dual power supplies and dual NICs (though generally to handle external
>> failures) and ECC-RAM but no hot-backup CPU or redundant RAM banks and...no
>> backup RAID card. Intel Enterprise SSD already have power-fail protection so I
>> don't need a RAID card to give me BBU. Given the MTBF of good enterprise SSD
>> I'm left to wonder if placing a RAID card in front merely adds a new point of
>> failure and scheduled-downtime-inducing hands-on maintenance (I'm looking at
>> you, RAID backup battery).
> 
> 
> 
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