Discuss April 2005

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234 participants
291 discussions

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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Re: [CentOS] Serial ATA hardware raid.
by Bryan J. Smith 16 Apr '05

16 Apr '05

From: Franki > After abit of searching, > I found a 4 port 8506 for retail $480 here: BTW, when I was estimating prices earlier, I was using US$. > For the record, this machine is to replace a web server with about 60+ domains hosted, I've been maintaining Linux DNS/SMTP servers since just before Apache surfaced, adding CERN httpd and the "patchy." But the majority of my Linux deployment has been for file servers - especially NFS as of 1999. I still prefer Fujitsu SPARC/Solaris and, even more so, NetApp filers as NFS/SMB plarforms, but throwing around TBph is typical. > some of which get allot of hits, > most are dynamic (Perl/PHP/Java) and the > server runs local MySQL/PostgreSQL as well. I feel very strongly about using RAID-0+1 in this configuration if you can afford to reduce your effective storage by 33% over RAID-5. But the choice is yours. You're not going to make a massive hit since CPU and network is more important. But you should still segment network and storage with an AMD8131 HyperTransport tunnel that provides seperate PCI-X channels for each. And don't skimp on the NIC - get something with at least 256KB SRAM receive cache. > I don't think speed is as important as redundancy, RAID-0+1 means you could possibly lose 2 discs and be okay, although there's no guarantee after losing 1. The other thing 3Ware does is read interleaving between the two mirrors. > but having said that, for future proofing, > I'd like to get a good performer as well. 3Ware's ASIC compared to a Microcontroller is like comparing a layer-2 ASIC+SRAM switch to a PC CPU+DRAM that does switching/routing. The ASIC can do it much faster, although the PC can buffer more. So it depends if you're just throwing data around like layer-2 switching (switching RAID-0, 1, 0+1 reads/writes), or if you are calculating dynamic routes in non-real-time (like RAID-5 XORs for parity). That's why 3Ware calls it a "storage switch." Of course if you have a 9500, it has DRAM too, so it's like having a layer-3 switch (that can route too). And without the inefficiency of the PC interconnect. > Which brings up another question, > I was looking at populating this thing > with 10,000 RPM 8MB cache 40gig (roughly) drives, > but the only drives I see in my pricelists that > match those specs are Western Digital Wd360GB's > and I generally have stayed away from WD drives in the > past due to dodgy standards implimentation > and the problems that can cause with Linux, First, other than Maxtor, Seagate and Hitachi, no one makes their own drives. WD taps the first and last for many, and Maxtor's approch is different than Seagate and Hitachi (I'll send you a link to any explaination). Secondly, the ATA drives *never* talk to the system, only the 3Ware ASIC. And unlike GPL Linux, 3Ware can get proprietary command set info from vendors. I have *never* had a "DMA timeout" in the history of my 6-year 3Ware usage. > should I continue to stay away? WD's 10,000rpm drives come off the same "enterprise" line as Hitachi's SCSI/SATA. They are not commodity at all. Hitachi and Seagate have dedicated "enterprise" lines for some SCSI/SATA, and then "commodity" lines for SCSI/SATA/ATA. Maxtor has only one line and then tests for tolerance and those that rate high are then declared "enterprise" with a 3-5 year warranty. > Actually, now that I think about it, > I guess 10,000 rpm drives with raid is probably over kill for my usage, Actually, since you are more concerned with latency in your application, then a faster spindle is better. In reality, the higher the density, typically the higher the DTR. So it is very common to see lower density or 1-gen back of higher spindles have a *lower* DTR than a lower spindle. > but they are pretty cheap anyway, (149 AUD each) but > if WD are still dodgy I have WD 40, 80 and 160 "consumer" ATA/SATA drives that give some chipsets fits under Linux, but 0 issues on a 3Ware card. > then I'd probably go for 7200rpm seagates > as I can get the 8MB 80gig 7200rpm drives for $85 AUD. Seagate is the only manufacture giving 3-5 year warranties on their "consumer" drives instead of 1-3. Yes, they cost 10-20% more than Maxtor/WD, but that's piece-of-mind IMHO. The "sweet spot" right now seems to be 200GB (160-250GB) for size, density (DTR performance) and price (sub-US$100). (4) 200GB = 400GB effective RAID-0+1. > Are Western Digitals still dodgy? All "integrated drive electronics" (IDE) drives via Advanced Technology (AT) Attachment (ATA) seem to do a poor job of following ATA-5 and ATA-6 specs. But with 3Ware, I've yet to have an issue. I even have 80GB WDs on old 3Ware 6000 series cards with 3-year-old firmware 6.9 that don't have an issue. BTW, 40C is the maximum ambient temperature a "consumer" SCSI/SATA/ATA drive should be exposed to. Drive life dives off if they run hotter. So consider getting a hot-swap enlosure that fits in a 3x5.25" bay that has 5 bays. They run $150.

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CentOS4 Loop at shutdown
by Collins Richey 16 Apr '05

16 Apr '05

Has anyone else encountered a loop and failure to shutdown on CentOS4? This has occurred twice in the past month, but unfortunately I failed to write down the looping messages. The only relevant problems I found via Google reference raid controllers, and I have POI (plain ol' IDE). Doh! Obviously I wuill need to record the errors. My environment is run-level 5 with GDM, but I use IceWm instead of one of the more common choices. IceWm shuts down cleanly. The loop occurs after selecting Shutdown from the GDM login panel. Errata are current as of last night. -- 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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Discuss April 2005