From mboxrd@z Thu Jan 1 00:00:00 1970 From: Doug Ledford Subject: Re: RAID 1 using SSD and 2 HDD Date: Thu, 28 Jul 2011 14:32:56 -0400 Message-ID: <4E31AB58.3030206@redhat.com> References: <4E25C9BA.1060401@dodtsair.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Roberto Spadim Cc: Mike Power , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 07/19/2011 02:27 PM, Roberto Spadim wrote: > no this not work very fast... > use bcache or other similar ssd+harddisk cache solution (facebook > have one solution i don=B4t remember the name) > mixing ssd and hdd are a big problem, since write speed is the slowes= t > (maybe ssd maybe hdd) and read speed isn=B4t very well since read in = ssd > can be non sequencial and at hdd sequencial is prefered, the read > balance algorithm is tuned to use the near position device, and > sometimes ssd isn=B4t used, or less used or more used... > a bigger speed can be done using a cache solution (ssd+hdd or ssd+rai= d1(hdd)) > that was my test results... maybe someone have others results You needed to use write-mostly, that would have drastically altered you= r=20 results. With write-mostly and write-behind enabled on the hard drives= ,=20 all reads go to the SSD instead of the hard drives, and writes complete= =20 as soon as the SSD says it is done and the writes to the hard drives=20 happen in the background. > > 2011/7/19 Mike Power: >> Is it possible to implement a RAID 1 array using two equal size HDD = and one >> smaller and faster SSD. The idea being that the resulting RAID woul= d have >> the same size of the HDD while picking up the speed benefits of the = SSD. >> You can do something similar today by just buying two hybrid drive= s and >> putting them in an array. By purchasing a dedicated SSD drive for t= hat >> purpose you gain the ability of controlling the size of the SSD port= ion. I >> was hoping the RAID array could use the SSD more as a cache then a r= edundant >> storage. >> >> Mike Power >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-raid= " in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html