From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Parschauer Subject: Re: [RFC] Process requests instead of bios to use a scheduler Date: Mon, 02 Jun 2014 13:12:18 +0200 Message-ID: <538C5C12.8060407@profitbricks.com> References: <5385DECE.5060507@profitbricks.com> <20140602093258.22aa2c05@notabene.brown> <538C4938.6010704@profitbricks.com> <20140602202050.14903534@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20140602202050.14903534@notabene.brown> Sender: linux-raid-owner@vger.kernel.org To: NeilBrown Cc: Linux RAID , =?ISO-8859-1?Q?Florian-Ewald?= =?ISO-8859-1?Q?_M=FCller?= List-Id: linux-raid.ids On 02.06.2014 12:20, NeilBrown wrote: > On Mon, 02 Jun 2014 11:51:52 +0200 Sebastian Parschauer > wrote: >> >> Nope, we have our RAID-1+0. So it is more or less a RAID-10 and >> putting the scheduler to this RAID-0 layer makes sense for us. > > I still cannot imagine how this would work. RAID-0 has no > decisions to make, so no where for a scheduler to fit. > > Just to clarify: is this md/raid0 over md/raid1 or md/raid0 over > hardware/raid1? We have both variants but tested the scheduler with servers without HW RAID and only 4 HDDs. On the production servers there are 24 HDDs, every 2 HDDs are in md/raid1 or HW RAID-1 and these 12 RAID-1 devices form an md/raid0 device. This is the only PV for LVM and LVs are the customer volumes exported via SCST/SRP. These are used by virtual machines on other servers. So the scheduler has to bring some fairness to the customer volumes so that a streaming customer can't block a database customer completely with his big sequential IOs as these would have priority. But our goal with a scheduler is to reduce latency for everyone. I hope this is clear, now. Just tell me if not. ;-)