Thread: software vs hw hard on linux
Due to various third party issues, and the fact PG rules, we're planning on migrating our deplorable informix db to PG. It is a rather large DB with a rather high amount of activity (mostly updates). So I'm going to be aquiring a dual (or quad if they'll give me money) box. (In my testing my glorious P2 with a 2 spindle raid0 is able to handle it fairly well) What I'm wondering about is what folks experience with software raid vs hardware raid on linux is. A friend of mine ran a set of benchmarks at work and found sw raid was running obscenely faster than the mylex and (some other brand that isn't 3ware) raids.. On the pro-hw side you have ones with battery backed cache, chacnes are they are less likely to fail.. On the pro-sw side you have lots of speed and less cost (unfortunately, there is a pathetic budget so spending $15k on a raid card is out of the question really). any thoughts? -- Jeff Trout <jeff@jefftrout.com> http://www.jefftrout.com/ http://www.stuarthamm.net/
My personal experience with RAID cards is that you have to spend money to get good performance. You need battery backedcache because RAID 5 only works well with write to cache turned on, and you need a good size cache too. If you don'thave it, RAID 5 performance will suck big time. If you need speed, RAID 10 seems to be the only way to go, but of coursethat means you are gonna spend $$s on drives and chasis. I wish someone would start a website like storagereview.comfor RAID cards because I have had _vastly_ differing experience with different cards. We currently havea compaq ML370 with a Compaq Smart Array 5300, and quite frankly it sucks (8MB/sec write). I get better performancenumbers off my new Tyan Thunder s2469UGN board with a single U320 10k RPM drive (50MB/sec) than we get off ourRAID 5 array including seeks/sec. Definately shop around, and hopefully some other folks can give some suggestions ofa good RAID card, and a good config. Alex Turner P.S. If there is movement for a RAID review site, I would be willing to start one, I'm pretty dissapointed at the lack ofresources out there for this. On Fri, Sep 12, 2003 at 10:34:26AM -0400, Jeff wrote: > Due to various third party issues, and the fact PG rules, we're planning > on migrating our deplorable informix db to PG. It is a rather large DB > with a rather high amount of activity (mostly updates). So I'm going to > be aquiring a dual (or quad if they'll give me money) box. (In my testing > my glorious P2 with a 2 spindle raid0 is able to handle it fairly well) > > What I'm wondering about is what folks experience with software raid vs > hardware raid on linux is. A friend of mine ran a set of benchmarks at > work and found sw raid was running obscenely faster than the mylex and > (some other brand that isn't 3ware) raids.. > > On the pro-hw side you have ones with battery backed cache, chacnes are > they are less likely to fail.. > > On the pro-sw side you have lots of speed and less cost (unfortunately, > there is a pathetic budget so spending $15k on a raid card is out of the > question really). > > any thoughts? > > -- > Jeff Trout <jeff@jefftrout.com> > http://www.jefftrout.com/ > http://www.stuarthamm.net/ > > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
threshar@torgo.978.org (Jeff) writes: > On the pro-sw side you have lots of speed and less cost (unfortunately, > there is a pathetic budget so spending $15k on a raid card is out of the > question really). I have been playing with a Perq3 QC card <http://www.scsi4me.com/?menu=menu_scsi&pid=143> which isn't anywhere near $15K, and which certainly seems to provide the characteristic improved performance. PriceWatch is showing several LSI Logic cards in the $300-$400 range with battery backed cache, which doesn't seem too out of line. It would seem a good tradeoff to buy one of these cards and drop a SCSI drive off the array. -- output = ("cbbrowne" "@" "libertyrms.info") <http://dev6.int.libertyrms.com/> Christopher Browne (416) 646 3304 x124 (land)
Jeff, > What I'm wondering about is what folks experience with software raid vs > hardware raid on linux is. A friend of mine ran a set of benchmarks at > work and found sw raid was running obscenely faster than the mylex and > (some other brand that isn't 3ware) raids.. Our company has stopped recommending hardware raid for all low-to-medium end systems. Our experience is that Linux SW RAID does as good a job as any $700 to $1000 RAID card, and has the advantage of not having lots of driver issues (for example, we still have one system running Linux 2.2.19 because the Mylex driver maintainer passed away in early 2002). The exception to this is if you are expecting to frequently max out your CPU and/or RAM with your application, in which case the SW RAID might not be so good because you would get query-vs.-RAID CPU contention. -- -Josh Berkus Aglio Database Solutions San Francisco
>>>>> "a" == aturner <aturner@neteconomist.com> writes: a> you need a good size cache too. If you don't have it, RAID 5 a> performance will suck big time. If you need speed, RAID 10 seems a> to be the only way to go, but of course that means you are gonna a> spend $$s on drives and chasis. I wish someone would start a I disagree on your RAID level assertions. Check back about 10 or 15 days on this list for some numbers I posted on restore times for a 20+ GB database with different RAID levels. RAID5 came out fastest compared with RAID10 and RAID50 across 14 disks. On my 5 disk system, I run RAID10 plus a spare in preference to RAID5 as it is faster for that. So the answer is "it depends". ;-) Both systems use SCSI hardware RAID controllers, one is LSI and the other Adaptec, all hardware from Dell. But if you're budget limited, spend every last penny you have on the fastest disks you can get, and then boost memory. Any current CPU will be more than enough for Postgres. -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Vivek Khera, Ph.D. Khera Communications, Inc. Internet: khera@kciLink.com Rockville, MD +1-240-453-8497 AIM: vivekkhera Y!: vivek_khera http://www.khera.org/~vivek/
>>>>> "J" == Jeff <threshar@torgo.978.org> writes: J> Due to various third party issues, and the fact PG rules, we're planning J> on migrating our deplorable informix db to PG. It is a rather large DB J> with a rather high amount of activity (mostly updates). So I'm going to If at all possible, batch your updates within transactions containing as many of those updates as you can. You will get *much* better performance. More than 2 procs is probably overkill. -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Vivek Khera, Ph.D. Khera Communications, Inc. Internet: khera@kciLink.com Rockville, MD +1-240-453-8497 AIM: vivekkhera Y!: vivek_khera http://www.khera.org/~vivek/
On Fri, 2003-09-12 at 07:34, Jeff wrote: > What I'm wondering about is what folks experience with software raid vs > hardware raid on linux is. A friend of mine ran a set of benchmarks at > work and found sw raid was running obscenely faster than the mylex and > (some other brand that isn't 3ware) raids.. I ended up going with a hybrid: RAID-1 across sets of two disks in hardware on Adaptec ZCR cards, and RAID-0 across the RAID-1s with Linux software RAID. Although the ZCR (2010 I believe) supports 0+1, using software striping turned in better performance for me. This way, I get brain dead simple dead disk replacement handled by hardware with some speed from software RAID. Also, I would think mirroring on the SCSI controller should take traffic off the PCI bus... <shrug> I have another machine that's stuck using a Compaq 5i plus controller with no battery backed write cache, in RAID 5. It sucks. Really bad. I'd rather use an IDE drive. :)