Return-Path: Delivered-To: apmail-cassandra-user-archive@www.apache.org Received: (qmail 64206 invoked from network); 14 Apr 2011 07:02:03 -0000 Received: from hermes.apache.org (HELO mail.apache.org) (140.211.11.3) by minotaur.apache.org with SMTP; 14 Apr 2011 07:02:03 -0000 Received: (qmail 59166 invoked by uid 500); 14 Apr 2011 07:02:00 -0000 Delivered-To: apmail-cassandra-user-archive@cassandra.apache.org Received: (qmail 59152 invoked by uid 500); 14 Apr 2011 07:02:00 -0000 Mailing-List: contact user-help@cassandra.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: user@cassandra.apache.org Delivered-To: mailing list user@cassandra.apache.org Received: (qmail 59143 invoked by uid 99); 14 Apr 2011 07:01:59 -0000 Received: from athena.apache.org (HELO athena.apache.org) (140.211.11.136) by apache.org (qpsmtpd/0.29) with ESMTP; Thu, 14 Apr 2011 07:01:59 +0000 X-ASF-Spam-Status: No, hits=1.5 required=5.0 tests=FREEMAIL_FROM,HTML_MESSAGE,RCVD_IN_DNSWL_LOW,SPF_PASS,T_TO_NO_BRKTS_FREEMAIL X-Spam-Check-By: apache.org Received-SPF: pass (athena.apache.org: domain of tmarthinussen@gmail.com designates 74.125.82.44 as permitted sender) Received: from [74.125.82.44] (HELO mail-ww0-f44.google.com) (74.125.82.44) by apache.org (qpsmtpd/0.29) with ESMTP; Thu, 14 Apr 2011 07:01:55 +0000 Received: by wwa36 with SMTP id 36so1411086wwa.25 for ; Thu, 14 Apr 2011 00:01:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type; bh=Yno5+S4+h8/Kn+MQqW+DMbM2nsAFmIR//ZFD9YeEqI0=; b=plaM7izSsI7lryxEU4mrpJMKZFZXXVamcP6Mj9BnAHwA5h5wG8j2yBZHBgJW8z/8zk ayA5VovBSMyu4EKquk+PQ409L25GU1Jv6JSfWNpXjr7xF/iIU4JEA9EiLB9Hx52d7q95 d+4umVIS5deRgL18Gz09j7t9qiz6YaLbvwJ5c= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=QaCx4ADvhnJcPaNhuVjPzh2k+NlzlmGVdkzjvzwsYxieuUyptiQn/+VVRp/5WGro90 FCscxN6Ye9ZtB0Z24Lwtv5wUmYoBVu6n2cW7ksQi+cmT/05szHF2U3zxjp2e5iBSJvyG BeZNZ0Dd8XOVqdjgrNog21gbFRkVTf0KyJHK8= MIME-Version: 1.0 Received: by 10.216.59.81 with SMTP id r59mr419329wec.40.1302764493771; Thu, 14 Apr 2011 00:01:33 -0700 (PDT) Received: by 10.216.81.9 with HTTP; Thu, 14 Apr 2011 00:01:33 -0700 (PDT) In-Reply-To: References: Date: Thu, 14 Apr 2011 16:01:33 +0900 Message-ID: Subject: Re: raid 0 and ssd From: Terje Marthinussen To: user@cassandra.apache.org Content-Type: multipart/alternative; boundary=000e0cdff822e0960e04a0db7ed4 --000e0cdff822e0960e04a0db7ed4 Content-Type: text/plain; charset=ISO-8859-1 Hm... You should notice that unless you have TRIM, which I don't think any OS support with any raid functionality yet, then once you have written once to the whole SSD, it is always full! That is, when you delete a file, you don't "clear" the blocks on the SSD so as far as the SSD goes, the data is still there. The latest SSDs are pretty good at dealing with this though, and some can be made a lot better by allocating extra spare block area for GC. Also be careful with raids and things like scrubbing or initialization of the Raid. This may very well "fill it 100%" :) Terje On Thu, Apr 14, 2011 at 2:02 PM, Drew Kutcharian wrote: > RAID 0 is the fastest, but you'll lose the whole array if you lose a drive. > One thing to keep in mind is that SSDs get slower as they get filled up and > closer to their capacity due to garbage collection. > > If you want more info on how SSDs perform in general, Percona guys have > done extensive tests. (In addition to comparing all the raid levels and etc. > > http://www.percona.com/docs/wiki/benchmark:ssd:start > > http://www.mysqlperformanceblog.com/2009/05/01/raid-vs-ssd-vs-fusionio/(see the "RELATED SEARCHES" on the right side too) > > - Drew > > > On Apr 13, 2011, at 9:42 PM, Anurag Gujral wrote: > > > Hi All, > > We are using three ssd disks with cassandra 0.7.3 , should we > set them as raid0 .What are the advantages and disadvantages of doing this. > > Please advise. > > > > Thanks > > Anurag > > --000e0cdff822e0960e04a0db7ed4 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hm...

You should notice that unless you have TRIM, which= I don't think any OS support with any raid functionality yet, then onc= e you have written once to the whole SSD, it is always full!

That is, when you delete a file, you don't "clear"= the blocks on the SSD so as far as the SSD goes, the data is still there.<= /div>

The latest SSDs are pretty good at dealing with th= is though, and some can be made a lot better by allocating extra spare bloc= k area for GC.

Also be careful with raids and things like scrubbing or= initialization of the Raid. This may very well "fill it 100%" :)=

Terje

On Thu, A= pr 14, 2011 at 2:02 PM, Drew Kutcharian <drew@venarc.com> wrote:
RAID 0 is the fastest, but you'll lose = the whole array if you lose a drive. One thing to keep in mind is that SSDs= get slower as they get filled up and closer to their capacity due to garba= ge collection.

If you want more info on how SSDs perform in general, Percona guys have don= e extensive tests. (In addition to comparing all the raid levels and etc.
http://www.percona.com/docs/wiki/benchmark:ssd:start

http://www.mysqlperformanceblog.com/2009/05/01/r= aid-vs-ssd-vs-fusionio/ (see the "RELATED SEARCHES" on the ri= ght side too)

- Drew


On Apr 13, 2011, at 9:42 PM, Anurag Gujral wrote:

> Hi All,
> =A0 =A0 =A0 =A0 =A0 =A0We are using three ssd disks with cassandra 0.7= .3 , should we set them as raid0 .What are the advantages and disadvantages= of doing this.
> Please advise.
>
> Thanks
> Anurag


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