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Re: [CentOS] Serial ATA hardware raid.
by Bryan J. Smith 18 Apr '05

18 Apr '05

From: Pasi Pirhonen > This is as good insertion point as anything else, > for what i am going to say. > 3ware is working like a champ, but slowly. > The tuning won't make it magically go over 100MB/s sustained writes. I am bumping up against 100MBps on my bonnie write benchmarks on an older 6410. Now that's in RAID-0+1, and not RAID-5. > Random I/O sucks (what i've seen) for any SATA-setup. It depends. "Raw" ATA sucks for multiple operations because it has no I/O queuing. AHCI is trying to address that, but it's still unintelligent. 3Ware queues reads/writes very well, and sequences them as best as it can. But it's still not perfect. > Even for /dev/mdX. Now with MD, you're starting to taxi your interconnect on writes. E.g., with Microcontroller or ASIC RAID, you only push the data you write. With software (including "FRAID"), you push 2x for RAID-1. That's 2x through your memory, over the system interconnect into the I/O and out the PCI bus. When you talk RAID-3/4/5 writes, you slaughter the interconnect. The bottleneck isn't the CPU. It's the fact that for each stripe, you've gotta load from memory through the CPU back to memory - all over the system interconnect, before even looking at I/O. For 4+ modern ATA disks, your talking a roundtrip that costs you an aggregate percentage of your system interconnect time beyond 30%+. On a dynamic web or other CPU computational intensive server, it matters little. The XOR operations actually use very little CPU power. And the web or computational streams aren't saturating the interconnect. But when you are doing file server I/O, and the system interconnect is used for raw bursts of network I/O as much as storage, it kills. > Puny oldish A1000 can beat those with almoust factor of ten for random I/O, but being limited to > max. 40MB/s transfers by it's interface (UW/HVD). Or more like the i960 because, after all, RAID should stripe some operations across multiple channels. > But what i am going to say is that for my centos devel work > (as in my NFS-server), i just recently moved my 1.6TB raid under /dev/md5 with > HighPoint RocketRaid1820. > I don't care that NOT being hardware RAID. > The /dev/mdX beats the 3ware 9500S-8 formerly used hands down when you > do have 'spare CPU cycles to let kernel handle the parity operations'. It has nothing to do with CPU cycles but interconnect. XOR puts no strain on modern CPUs, it's the added data streams being feed from memory to CPU. Furthermore, using async I/O, MD can actually be _faster_ than hardware RAID. Volume management in an OS will typically do much better than a hardware RAID card when it comes to block writes. Of course the 9500S is still maturing. Which is why I still prefer to use 4 and 8 channel 7506/8506 cards with RAID-0+1. Even the AccelATA and 5000 left much to be desired before the 6000 and latter 7000/8000 series.

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mod_authz_svn anyone?
by Howard Fore 18 Apr '05

18 Apr '05

Hey, Anyone know where I can find the Apache module mod_authz_svn? I'm trying to setup a subversion repository and would like to use that module for the authentication. yum doesn't find anything. Thanks. -- Howard Fore, howard.fore(a)gmail.com

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Software RAID on CentOS 4
by centos.org_list＠000a.com 18 Apr '05

18 Apr '05

All this talk about SATA RAID in the past few days made me wonder... about possibly using software RAID, or at least trying it on my own workstations and eventually production servers, after I learn more about it. So, I started googling for tutorials and manuals, and there are usually two kinds I can find: 1. very basic "what is software RAID", or 2. complete 400+ page books on the topic sold at Amazon.com Nothing in between. :-( Does anyone know of a good resource where I could read up more on it, from properly setting up boot drives (and mirroring boot partitions to second drive in RAID-1 config), to setting up swap partition, to best practices, caveats, etc. All these articles usually also lack any kind of disk/data recovery info, procedures for detecting and swapping failed drives, etc. I'm mostly interested in simple RAID-1 for redundancy - just 2 drives per system, that's all. Typically on my hardware RAID boxes I set up a /boot, swap and / partitions, and would like to do the same using software RAID - again, with the ability to have a fully working boot partition and complete filesystem in case the main drive fails. Thanks for any pointers, whether online or off. I'm not adverse to buying a 400+ page book if it covers all this, but the books I came across so far had pretty bad reviews and lacked data recovery altogether, which would make them rather useless. Chris

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inotify on rhel systems?
by Collins Richey 17 Apr '05

17 Apr '05

I just read an interesting article caleed "Monitor Linux file system events with inotify.", see http://www-128.ibm.com/developerworks/linux/library/l-inotify.html?ca=dgr-l…. I notice that /dev/inotify is not present on my CentOS4 system, so the necessary kernel patches are probably not present. Does anyone know if there are any plans afoot to provide this functionality for rhel systems? -- Collins When I saw the Iraqi people voting three weeks ago, 8 million of them, it was the start of a new Arab world.... The Berlin Wall has fallen. - Lebanese Druze leader Walid Jumblatt

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CentOS4 upgradeany hangs while loading sata_via
by Norbert Kiesel 17 Apr '05

17 Apr '05

Hi, I have a machine running under CentOS 3.4 which I want to upgrade to CentOS 4. I booted using the CentOS 4 CD1 using "linux upgradeany". Problem is that loading sata_via never terminates. Ismod shows the sata_via module in state "Loading" while all others are in state "Live". The dmesg output shows that the module gets loaded, sees two disks, then prints info about the first one and is stuck there. I can of course provide the exact output if needed, but I would have to write it down by hand as the machine has no floppy and I can't write to the hard disk :-( Any ideas? I fear that if I just upgrade through yum, the machine won't boot afterwards. As this is one of our production DB machines, I'd rather not do that. Would compiling a kernel on my own with a newer version of sata_via and using that module be something worth trying? Best, Norbert

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Re: [CentOS] Serial ATA hardware raid.
by Bryan J. Smith <b.j.smith＠ieee.org> 17 Apr '05

17 Apr '05

From: Harald Finnï¿½s <spamcatcher(a)lantrix.no> > If memory serves, I had the worst performance on aa 7506-8 running R5 and > MDK 10.1. Write performance was extremenly slow, so the box would use all > memory for cache almost immidiately. This resulted in very high CPU, and > the machine became unresponsive. After applying: > sysctl -w "vm.bdflush=0 500 0 0 500 3000 0 20 0" > it was back to normal. This works with 2.4 kernels only. Correct, because the Linux kernel is tuned to assume the storage does NOT provide I/O queuing. As I stated in another e-mail, the Linux kernel does async I/O by default. Some cards, like the 3Ware, try to sync I/O as best as it can for safety. This hurts performance quite a bit -- especially on the 9000 series. The 9000 series now introduces DRAM, and by default, isn't battery backed on the 9000 (the kits just became available), hence the defaults that are very "sync-like." I _highly_recommend_ you change those defaults (and get the kit too). All prior 3Ware cards are SRAM-only, which does not require an external battery source. DRAM is a leaky cell that uses 100x+ the power of SRAM, which is a complex, combinational circuit. That's why prior 3Ware cards didn't need external battery, they use SRAM. You can typically cycle power and the 3Ware write cache will be flushed (at least on the 7000/8000 series). > With 2.6 this improves performance: > blockdev --setra 16384 /dev/sda > I'm pretty sure I found both these setting in the 3ware knowledgebase. So many people don't hit the 3Ware knowledge base. You should *ALWAYS* hit the knowledge base of your intelligent card vendor. Remember, the Linux kernel is tuned to assume storage controllers unintelligent and have *0* I/O queuing capability. Hence why LVM/MD is "tuned out of the box" with Linux. Furthermore, the SCSI-2 protocol provides standard command-sets for I/O queuing for SCSI cards, as well as Intel's I2O (dpt_i2o). But when you have a "generic" SCSI block driver, like with 3Ware and many others (including the DAC_960 for a few older Mylex cards), you need to tell the kernel's VM and block interface how to best stages writes and other operations. -- Bryan J. Smith mailto:b.j.smith@ieee.org

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Re: [CentOS] Serial ATA hardware raid.
by Bryan J. Smith <b.j.smith＠ieee.org> 17 Apr '05

17 Apr '05

From: Les Mikesell <lesmikesell(a)gmail.com> > Note that software mirroring has some advantages too and is not > a big performance hit as long as the underlying hardware uses > DMA and works independently (i.e. don't do it with drives > on the same IDE controller cable). Actually, I wouldn't do it on the same PCI bus. With drives able to burst at 50MBps, the amount of traffic on your interconnect can actually be high. > I consider it a big plus to be able to take a drive from a mirrored pair, plug > it into just about any computer without worrying about having > exactly the same brand of controller, and recover the data - or > take over the service the broken computer was providing. Then you'll like 3Ware. For RAID-1, it doesn't change the organization. But even if you use RAID-0, 0+1 and RAID-5, the great thing about 3Ware is you _can_ safely move the drives to _any_ model card, as long as the firmware is at least the same or newer. I have done this with volumes from 5000 to 6000 or 7000, 6000 to 7000. > And by the way, there's nothing wrong with running a DNS server > and mail server on the same machine - but you should have a 2nd > dns server which can also provide other services. A secondary mail server is always a good idea too. Ideally, you should consider a chroot environment or even an UML instance for each. > You might need a bit more RAM but DNS typically is not a big cpu load. But you are correct from a load standpoint, neither will hit you too much. -- Bryan J. Smith mailto:b.j.smith@ieee.org

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CentOS4 ok on Dell cerc sata raid ?
by Francois Caen 17 Apr '05

17 Apr '05

Hello, There's been a lot of talk lately about raid controllers :-) I'm thinking about buying a Dell Poweredge with the Dell CERC SATA RAID Controller, 64MB Cache. It'll be either a P4 or a 64bit Xeon. Does CentOS4 recognize these controllers fine? Any extra driver needs to be installed? Thanks, Francois

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Test kernel for a certain feature
by Mário Gamito 16 Apr '05

16 Apr '05

Hi, Is there a command one can issue to check if the kernel supports a certain feature ? Let's say, for instance, Appletalk, or NTFS. Whatever... Warm Regards, Mário Gamito

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Serial ATA hardware raid.
by Franki 16 Apr '05

16 Apr '05

Hi everyone, I'm looking into setting up a SATA hardware raid, probably 5 to use with CentOS 4. I chose hardware raid over software mostly because I like the fact that the raid is transparent to the OS. Does anyone know of any SATA controllers that are well tested for this sort of usage? From what I can tell from googling, this is more or less where RHEL stands: Red Hat Enterprise Linux version 3 and the current version of Fedora support the following SATA chipsets: Intel's ICH5 SATA chipset Silicon Image's SATA chipset Does CentOS4 add anything to this as it is based on 2.6 kernel? My question upon reading what I found on Google, is if it is true hardware raid, shouldn't the OS not be able to tell it's raid at all? I'm assuming that the chipsets listed above are driver based hardware raid? what I am after is a raid array based on true hardware raid such that the OS see's just one drive, and the hardware firmware handles any mirror/striping. Any suggestions? regards Franki

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