From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marian Csontos Subject: Re: Balanced Striping Date: Thu, 20 Feb 2014 13:10:19 +0100 Message-ID: <5305F0AB.7060100@redhat.com> References: Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1"; Format="flowed" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development , heiligerstein@gmail.com List-Id: dm-devel.ids On 02/18/2014 08:34 PM, Leonardo Santos wrote: > I'm trying to make a experimental balance striping between SSD and HDD > based on some performance parameter (latency or throughput) gotten on the > fly. > > I realized that when I increase the number of operations for SSD (e.g. 3x= 1, > SSDxHDD) it doesn't give me the better of both. > > My HDD read sequentially at ~100MB/s and my SSD at ~400MB/s. My hope is > throughput to be the sum of SSD and HDD, but this its not true for my tes= ts. > > For instance, when I put operations in 1x1: > SSD =3D ~100MB/s > HDD =3D ~100MB/s > > When I put 3x1: > SSD =3D ~150MB/s > HDD =3D ~50MB/s (why its not 100MB/s?) Not sure what you are trying to achieve and if you really need this or = just want to misuse DM to fit your goals. 1. Let's answer the "Why?" question Are you trying to implement kind of I/O shaping or throttling? = (Otherwise I do not understand the need to cripple the SSD speed by = using it in such a configuration, but anyway...) 2. Then we can either move to "How?" Would cgroups work for you? > > For me its not parallel, but only distributes the operations in a > proportional way. > > Questions: > - Why isn't throughput equal to HDD + SSD in normal mode (1x1)? > - Why HDD reduces proportionally? > - Its not parallel? Where can I change it to make this parallel? 3. Or to your "Why?" questions. For that I have no answers, just questions: - How do you measure the throughput? (Exact command would be the best.) - How are the disks connected? (Is this single SSD you divided into = partitions and are now hitting it with 3x more IOPS while the reads are = not sequential anymore which _should_ not have much effect) - What's the throughput when using striped SSD(s) only? - What does `dmsetup status` says? - What are sector sizes? Chunk sizes? and Block sizes you read? > > I using this in my research and changed dm-stripe.c. > > Thanks a lot! > > *Leonardo Ant=F4nio dos Santos* > > > > -- > dm-devel mailing list > dm-devel@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel >