From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mr213139.mail.yeah.net ([223.252.213.139]) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1bah4O-0008Tv-V4 for linux-mtd@lists.infradead.org; Fri, 19 Aug 2016 10:30:43 +0000 Subject: Re: MTD RAID To: Richard Weinberger , Boris Brezillon References: <20160819084908.4955c629@bbrezillon> <57B6B073.9060404@easystack.cn> <20160819102016.0640b6d5@bbrezillon> <57B6CC7B.1060208@easystack.cn> Cc: starvik@axis.com, jesper.nilsson@axis.com, Dongsheng Yang , linux-cris-kernel@axis.com, shengyong1@huawei.com, Ard Biesheuvel , David Woodhouse , dmitry.torokhov@gmail.com, dooooongsheng.yang@gmail.com, jschultz@xes-inc.com, fabf@skynet.be, mtownsend1973@gmail.com, linux-mtd@lists.infradead.org, Colin King , asierra@xes-inc.com, Brian Norris , Dongsheng Yang From: Dongsheng Yang Message-ID: <57B6DFB5.8000208@easystack.cn> Date: Fri, 19 Aug 2016 18:30:13 +0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hi Richard. On 08/19/2016 05:47 PM, Richard Weinberger wrote: > Yang, > > Sorry when I ask already answered questions, the mail thread > grows faster than I can type. ;) > > On 19.08.2016 11:08, Dongsheng Yang wrote: >> But how can we handle the multiple chips problem? Some drivers >> are combining multiple chips to one single mtd device, what the >> mtd_concat is doing. > mtd_concat is a horrid and old hack which was used to combine very > small flashes. > >>> One last question? What's the real goal of this MTD-RAID layer? If >>> that's about addressing the MLC/TLC NAND reliability problems, I don't >>> think it's such a good idea. >> Oh, that's not the main problem I want to solve. RAID-1 is just a possible >> extension base on my RAID framework. >> >> This work is started for only RAID0, which is used to take the use of lots >> of flash to improve performance. Then I refactored it to a MTD RAID >> framework. Then we can implement other raid level for mtd. >> >> Example: >> In our production, there are 40+ chips attached on one pcie card. >> Then we need to simulate all of them into one mtd device. At the same >> time, we need to consider how to manage these chips. Finally we chose >> a RAID0 mode for them. And got a great performance result. >> >> So, the multiple chips scenario is the original problem I want to solve. And >> then I found I can refactor it for other RAID-levels. > Are your chips NAND flash? > Combining non-NAND is not that hard, mtd_concat does already. > With NAND, as Boris pointed out, it will become complicated. Yes, it's NAND, but I think this layer will be working for all MTD devices. > > So, what you propose as MTD RAID is not really RAID. > RAID is about redundant disks. i.e. you can replace them upon failure. > The problem you address is combining multiple chips. > IOW an SSD emulated in software. Yes, the original idea is from it, but I am wishing to implement a real RAID for mtd now. Although we are only using RAID0 in our production. I am glad to implement other RAID-levels in community. And yes, sounds not easy for NAND devices. But I will to figure out the solutions for these problems Boris pointed out. BTW, what's the other idea to solve the reliability problem in MLC currently in community. Yang > > I think we don't need replication on MTD. An improved mtd_concat > does not sound bad but a proper implementation has to deal with > all the nastiness of NAND. > > Thanks, > //richard > > ______________________________________________________ > Linux MTD discussion mailing list > http://lists.infradead.org/mailman/listinfo/linux-mtd/ >