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• Creating mdraid device on top of other existing mdraid devices

  - by Dmitriusan

  I'm considering creating something like "hierarchical raid" and wondering whether it is possible using pure mdraid. Moreover, I'm going to boot from this device. I'm using Ubuntu Server 12.04 LTS with Grub2 bootloader. Motivation behind doing that is: I have 4 x 1tb 7200rpm disks. Two are newer and faster (up to 200mb/sec) and other two are slower (up to 140mb/sec). I want to create RAID-0 device from them. When creating such RAID-0 directly from 4 hard disks, I get summary speed up to ~480mb/sec. That is roughly 4*120mb/sec, so RAID-0 works with speed of the slowest device. I have an idea to create a separate RAID-0 md0 device from 500gb partitions of slower hard disks. Theoretically, this md0 device will have speed 2*140=240~280mb/sec. After that, I'm going to add this md0 device to RAID-0 with faster disks, finishing with up to 3*200=600mb/sec. Stripe-width for this raid will be 2x times bigger than for underlying raid with slow disks. Questions are: is it possible or I'm missing something? will that work as expected? can I boot from such consolidated raid device? any better ideas? any pitfalls? I don't want to use fakeraid for consolidating slow disks for multiple reasons (portability, ability to customize parameters and so on). PS Speed is needed for home virtualization server and just for experience/fun. Reliability is provided via regular automatic backups to a separate device. PPS I considered also using different stripe-width for hard disks with different speed in single raid, but mdraid does not seem to support that.

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• Need advice on which PCI SATA Controller Card to Purchase

  - by Matt1776

  I have a major issue with the build of a machine I am trying to get up and running. My goal is to create a file server that will service the needs of my software development, personal media storage and streaming/media server needs, as well as provide a strong platform for backing up all this data in a routine, cron-job oriented German efficiency sort of way. The issue is a simple one - all my drives are SATA drives and my motherboard controller only contains 4 ports. Solving the issue has proven to be an unmitigated nightmare. I would like advice on the purchase of the following: 4 Port internal SATA / 2 Port external eSATA PCI SATA Controller Card that has the following features and/or advantages: It must function. If I plug it in and attach drives, I expect my system to still make it to the Operating System login screen. It must function on CentOS, and I mean it must function WELL and with MINIMAL hassle. If hassle is unavoidable, there shall be CLEAR CUT and EASY TO FOLLOW instructions on how to install drivers and other supporting software. I do not need nor want fakeRAID - I will be setting up any RAID configurations from within the operating system. Now, if I am able to find such a mythical device, I would be eternally grateful to whomever would be able to point me in the right direction, a direction which I assume will be paved with yellow bricks. I am prepared to pay a considerable sum of money (as SATA controller cards go) and so paying anywhere between 60 to 120 dollars will not be an issue whatsoever. Does such a magical device exist? The following link shows an "example" of the type of thing I am looking for, however, I have no way of verifying that once I plug this baby in that my system will still continue to function once I've attached the drives, or that once I've made it to the OS, I will be able to install whatever drivers or software programs I need to make it work with relative ease. It doesn't have to be dog-shit simple, but it cannot involve kernels or brain surgery. http://www.amazon.com/gp/product/B00552PLN4/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B003GSGMPU&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1HJG60XTZFJ48Z173HKY So does anyone have a suggestion regarding the subject I am asking about? PCI SATA Controller Cards? It would help if you've had experience with the component before - that is after all why I am asking here - for those who have had experience that I do not have. Bear in mind that this is for a home setup and that I do not have a company credit card. I have a budget with a 'relative' upper limit of about $150.00.

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• Weird nfs performance: 1 thread better than 8, 8 better than 2!

  - by Joe

  I'm trying to determine the cause of poor nfs performance between two Xen Virtual Machines (client & server) running on the same host. Specifically, the speed at which I can sequentially read a 1GB file on the client is much lower than what would be expected based on the measured network connection speed between the two VMs and the measured speed of reading the file directly on the server. The VMs are running Ubuntu 9.04 and the server is using the nfs-kernel-server package. According to various NFS tuning resources, changing the number of nfsd threads (in my case kernel threads) can affect performance. Usually this advice is framed in terms of increasing the number from the default of 8 on heavily-used servers. What I find in my current configuration: RPCNFSDCOUNT=8: (default): 13.5-30 seconds to cat a 1GB file on the client so 35-80MB/sec RPCNFSDCOUNT=16: 18s to cat the file 60MB/s RPCNFSDCOUNT=1: 8-9 seconds to cat the file (!!?!) 125MB/s RPCNFSDCOUNT=2: 87s to cat the file 12MB/s I should mention that the file I'm exporting is on a RevoDrive SSD mounted on the server using Xen's PCI-passthrough; on the server I can cat the file in under seconds ( 250MB/s). I am dropping caches on the client before each test. I don't really want to leave the server configured with just one thread as I'm guessing that won't work so well when there are multiple clients, but I might be misunderstanding how that works. I have repeated the tests a few times (changing the server config in between) and the results are fairly consistent. So my question is: why is the best performance with 1 thread? A few other things I have tried changing, to little or no effect: increasing the values of /proc/sys/net/ipv4/ipfrag_low_thresh and /proc/sys/net/ipv4/ipfrag_high_thresh to 512K, 1M from the default 192K,256K increasing the value of /proc/sys/net/core/rmem_default and /proc/sys/net/core/rmem_max to 1M from the default of 128K mounting with client options rsize=32768, wsize=32768 From the output of sar -d I understand that the actual read sizes going to the underlying device are rather small (<100 bytes) but this doesn't cause a problem when reading the file locally on the client. The RevoDrive actually exposes two "SATA" devices /dev/sda and /dev/sdb, then dmraid picks up a fakeRAID-0 striped across them which I have mounted to /mnt/ssd and then bind-mounted to /export/ssd. I've done local tests on my file using both locations and see the good performance mentioned above. If answers/comments ask for more details I will add them.

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