From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: SSD & mechanical disc in RAID 1 Date: Mon, 01 Feb 2010 15:06:32 -0500 Message-ID: <4B673448.4080002@tmr.com> References: <7a329d911001090953j17829cd9qca0888fbcd7b4805@mail.gmail.com> <20100109192326.GB16383@rap.rap.dk> <87bpgmyu37.fsf@frosties.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <87bpgmyu37.fsf@frosties.localdomain> Sender: linux-raid-owner@vger.kernel.org To: Goswin von Brederlow Cc: Keld Jorn Simonsen , Wil Reichert , linux raid List-Id: linux-raid.ids Goswin von Brederlow wrote: > Keld J=F8rn Simonsen writes: > > =20 >> On Sat, Jan 09, 2010 at 09:53:11AM -0800, Wil Reichert wrote: >> =20 >>> Has anyone ever tried putting an SSD and a mechanical disc in RAID = 1 >>> using write-mostly? The goal would be to extol the speed & latency >>> virtues of an SSD while retaining the integrity of the traditional >>> storage. Would this setup even work as I expect it to? >>> =20 >> I think you are better served by trying out RAID10 in the far or off= set >> layouts. RAID1 would per se not gain from the low latency times of=20 >> SSD. RAID1 should function the same with hard disk as with SSD,=20 >> and with hard disk it would not make sense to multiplex reading >> of a file, as skipping and reading a block essentially takes the sam= e >> time. >> >> Best regards >> Keld >> =20 > > With raid10 in the far or offset layout every (large) read and write > would always access both the SSD and rotating disk. That would make > every operation wait for the rotating disk to seek. > > > I think his initial idea of raid1 is verry good. With write-mostly al= l > reads should come from the fast SSD. I would also add write-behind. > That way writes will not wait for the rotating disk and get the full > SSD speed as well. > =20 I had an SSD waiting to be deployed, and I tried putting a journal on i= t=20 and using a mount with data=3Djournal. Supposedly when the data is writ= ten=20 to the journal the write will be "complete" and effective write speed=20 for many small random writes will be higher. I don't have the results=20 handy, but they were not so great that I went out and got another SDD. --=20 Bill Davidsen "We can't solve today's problems by using the same thinking we used in creating them." - Einstein -- 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