Date: Sat, 30 Oct 2010 20:34:54 +0200 From: =?iso-8859-1?Q?Peter_Ankerst=E5l?= <peter@pean.org> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: freebsd-fs@freebsd.org Subject: Re: Raid + zfs performace. Message-ID: <34DA1356-9622-43C0-BA41-61E4A14C6533@pean.org> In-Reply-To: <20101030182346.GA61519@icarus.home.lan> References: <D2954020-C3A0-46EC-8C64-EB57EA1E9B21@pean.org> <AANLkTinQWchAPtcqcO3mDt9gKK5tCsHo8khyiD69M4BV@mail.gmail.com> <86693036-9351-4303-BADA-C99F7A4C375C@pean.org> <20101030182346.GA61519@icarus.home.lan>
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On 30 okt 2010, at 20.23, Jeremy Chadwick wrote: > On Sat, Oct 30, 2010 at 07:56:56PM +0200, Peter Ankerstål wrote: >> >> >> On 30 okt 2010, at 19.39, Sean wrote: >> >>>> I have a question about raid and zfs. I Have a hardware-raid running. >>>> A mirror thats the only storage in my zfs pool. Im going to >>>> add another mirror to the machine and my question is, what is the best option performace-wise? >>> >>> The best performance option is to get rid of the hardware-raid, and >>> present each disc to ZFS in a JBOD fashion. >> >> Ok. RIght now thats not an option. I have a da0 device thats a hardware-raid mirror. and it is currently >> the only device in the only pool on the machine. >> >>> >>>> Is it to add the other mirror to the same pool or create another separate pool for that mirror? >>>> Btw. Today my disk are quite saturated r/w wise. >>> >>> RAID functionality only exists within the context of a single pool. >>> You don't create a new pool and then try to mirror the two pools. You >>> add the storage to an existing pool, unless you have a reason to start >>> a new pool. When I already have a mirror, I like to add new mirror >>> sets. It's the equivalent of a RAID 10 scenario. >> >> Yes I know. >> I thought maybe because the existing pool is kind of r/w saturated it should be better >> to create a new independent pool for the new drives. In that way the heavy activity >> would not "spread" to the new drives. >> >> Now you presented me with a third option. So you think I should skip to create >> a new hardware-raid mirror and instead use two single drives and add these as >> a mirror to the existing pool? How will zfs handle howswap of these drives? >> I've seen a few crashes due to ata-detach in other systems. > > As stated previously: ideally you should turn off all RAID capabilities > on the controller itself and just use JBOD + let FreeBSD deal with the > RAID'ing (in this case, ZFS). > > I realise you can't do this for the current hardware RAID'd "da0" > mirror. I also understand the reason you might have done this. I too > would trust a hardware RAID controller to handle booting from a mirror > more than the FreeBSD bootstraps. (I choose not to deal with things > like gptzfsboot, zfsloader, etc. etc. -- these should all just become > part of the standard bootstraps and stop requiring people to jump > through hoops to achieve such capabilities) > Yes. > As for hot-swapping of drives: there are well-established procedures for > this sort of thing. I blogged about it[1] not too long ago, with > real-world server hardware. I think it will address your concerns, > since I spent the time to document *everything*, including all output. > > What confuses me about your statement is that you're talking about > "ata-detach" when your drives are appearing as daX, which implies use of > CAM. Are you talking about hot-swapping failing on a completely > different system which was using ata(4) without AHCI? If so, I'm not > surprised. You need AHCI to achieve this. Yes, that was another machine. > > Finally, you should be aware that there are two AHCI "methods" > implemented in FreeBSD: ataahci.ko and ahci.ko. ataahci is the older of > the two and uses ata(4). ahci.ko is the newer of the two and is > significantly better, since it makes use of CAM, and thus provides > performance improvements and handles hot-swapping a lot better (IMHO). > ahci.ko "trumps" ataahci.ko (meaning if your kernel includes ataahci and > you do "load ahci" from loader or loader.conf, ahci.ko will be used > instead). Be aware that ahci.ko disks appear as adaX (this is not a > typo). > > [1]: http://koitsu.wordpress.com/2010/07/22/freebsd-and-zfs-hot-swapping-sata-disks-with-ahci/ > > -- > | Jeremy Chadwick jdc@parodius.com | > | Parodius Networking http://www.parodius.com/ | > | UNIX Systems Administrator Mountain View, CA, USA | > | Making life hard for others since 1977. PGP: 4BD6C0CB | > >
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