Jon Bendtsen wrote: > Ron Arts wrote: > [snip] (I received your report, thanks) > > >>Results are below. Anyone care to comment? Especially LVM performance >>disappointed here. > > > I cant clearly see what is LVM setup and what isnt. Remember that LVM > doesnt allocate blocks sequeltial, but by default the first one free. > So, when you create 3 lv's, and then you mkfs them, then you allocate > at least the first block. Then when you fill the rest of the > filesystem... > you allocate the next blocks. Results are one block in the beginning, > a wide gap, and then the rest of the blocks. > Sorry, I don't understand. Why the gap? Omn the other hand, the underlying devices are RAID-1 in software, the allocation shouldn't matter should it? > > >>LVM machine setup: >> >>2 18Gb disks. I created 3 partitions on both disks, 128Mb, 512Mb and 17Gb >>Equal partitions were combined into RAID-1 devices (md driver). >>First md device mounted on /boot, second for swapfile, and third >>as basis for LVM >> >>Out of the volume group four LV were created and mounted as follows: >> >>[root@nbs-126 root]# df >>Filesystem 1K-blocks Used Available Use% Mounted on >>/dev/vg0/root 4225092 1293064 2717400 33% / >>/dev/md0 124323 11517 106387 10% /boot >>/dev/vg0/home 4225092 32828 3977636 1% /home >>none 514996 0 514996 0% /dev/shm >>/dev/vg0/var 4225092 51720 3958744 2% /var >>/dev/vg0/mysql 16513960 32828 15642272 1% /var/lib/mysql >> >>Is there a reason for the performance degradation I saw with LVM? > > > I've done 3 (or 0.5 + 0.5 + 1) benchmarks. The first 2 times i didnt do > it well enough. I dont believe you have done it well enough, you clearly > dont have enough numbers. I found that using tiobench i had to variate > the number of threads (concurrent read/write) and the blocksize, before > i > got the best performance. And it variates alot. (See my .pdf, which i > will > mail to you). I've got lots of numbers. I used gnuplot to create graphs, Okay, but lots of numbers still don't explain why in this particular case performance was so slow. If I understand why, I can begin to make optimizations. To give some background: I do this because I need such a setup for a particular application (MySQL high volume logging server). If I understand the issues involved I can make more informed choices implementing the application. Should it log using multiple threads or one? Will readers from the datbase hinder the writing process a lot? What is the best way to add disks using LVM, without taking a large performance hit? This server must be up 24x7. I found something called scsirastools that can deal with hotswapping SCSI disks under software RAID. I thought I'd first try some benchmarks with bonnie to get a feel for the issues involved, and seeing the performance (and CPU) hit for my LVM setup (and having never used LVM before) I decided to ask you guys about this. And thanks for your report, at least it confirmed what I had seen: software raid is faster then hardware. Regards, Ron Arts -- Netland Internet Services bedrijfsmatige internetoplossingen http://www.netland.nl Kruislaan 419 1098 VA Amsterdam info: 020-5628282 servicedesk: 020-5628280 fax: 020-5628281 Does old mail ever arrive?
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