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Re: Any issues running Linux from SSD on laptop?
by Toby Corkindale 04 Nov '12

04 Nov '12

On 05/11/12 10:35, hannah commodore wrote: > On 05/11/2012, at 10:07, Toby Corkindale <toby.corkindale(a)strategicdata.com.au> wrote: > >> There are some tools around that'll benchmark different block sizes >> to work out the appropriate value, too. However note that this issue >> only seemed to be a *big* issue for earlier generation SSDs.. the >> current ones seem to cope pretty well regardless. > > What are these utils? Have you used them? > I always have difficulty aligning blocks when installing new machines, and would love to get more insight into the operation and its effects It's been a little while since I used them, but yeah, I have. I think this was the tool I used: https://github.com/bradfa/flashbench

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Re: cache, Xen, and zfsonlinux
by Craig Sanders 02 Nov '12

02 Nov '12

On Sun, Oct 14, 2012 at 09:01:49PM -0700, Daniel Pittman wrote: > On Sun, Oct 14, 2012 at 7:25 PM, Russell Coker <russell(a)coker.com.au> wrote: > > I'm looking at converting some Xen servers to ZFS. This includes a > > couple of servers for a reasonable size mail store (8,000,000 files > > and 600G of Maildir storage). > > > > For much of the Xen on ZFS stuff I'll just use zvols for block > > devices and then use regular Linux filesystems such as Ext3 inside > > them. This isn't particularly efficient but for most DomUs it > > doesn't matter at all. Most of the DomUs have little disk access > > as they don't do much writing and have enough cache to cover most > > reads. > > > > For the mail spool a zvol would be a bad idea, fsck on a 400G Ext3/4 > > filesystem is a bad thing and having the double filesystem overhead > > of Ext3/4 on top of a zvol is going to suck for the most disk > > intensive filesystem. > > zvol is more like an LVM logical volume than a filesystem, so the > overhead isn't nearly as much as this comment suggests. yep. > That said, running ext3 (especially) or ext4 on top of it is going to > be slower, and means you can't use the RAID style features of ZFS, and > you give up object level checksums. that's not exactly true - the guest won't know anything about the ZFS features, but the ZFS file-server certainly will....the zvol will be a chunk of allocated space from one of the zpools on the system. it can optionally be sparse-allocated (for thin-provisioning, greatly reduces space used, but performance can suffer). The zvol has all the benefits of the zfs pool, including snapshotting and cloning, COW, error checking and recovery, SSD read and write caching. The zvol can be backed up (or moved to another ZFS server) with 'zfs send' & 'zfs receive'. It can also be exported as an iscsi volume (e.g. so that a remote virtualisation cpu node can access the volume storage on the zfs file server). cloning is particularly useful for VMs - in short, set up a 'template' VM image, clean it up (e.g. run 'apt-get clean', delete /etc/udev/rules.d/70-persistent-net.rules, and so on), snapshot it, and then clone the snapshot whenever you need a new VM. you could even, for example, build a squeeze 6.0 VM template, snapshot it, then later boot it up and upgrade to 6.01, 6.02, ..., 6.06, and have a cleaned up snapshot of each point-release, any of which could be cloned into a new VM at any time. >From the guest VM's point-of-view, it's just a disk with nothing special about it. ext3 or ext4 performance in the guest will be similar to performance if the guest were given an LVM lv. I haven't done any benchmarking to compare zvol with lv (mostly because and I can't afford to add 4 drives to my ZFS server just to test LVM lv vs ZFS zvol performance), but I can give a subjective anecdote that the performance improvement from using a ZFS zvol instead of a qcow2 disk image is about the same as using an LVM lv instead of a qcow2 file. i.e. *much* faster. if i had to guess, i'd say that there are probably some cases where LVM (with its nearly direct raw access to the underlying disks) would be faster than ZFS zvols but in most cases, ZFS' caching, compression, COW and so on would give the performance advantage to ZFS. ZFS's other advantages, especially lightweight and unlimited snapshots, make it worth using over LVM anyway. FYI, here are the details on one of several zvols of various sizes that I have on my home ZFS server. They're all used by KVM virtual machines. # zfs get all export/sid NAME PROPERTY VALUE SOURCE export/sid type volume - export/sid creation Sun Mar 25 14:19 2012 - export/sid used 5.16G - export/sid available 694G - export/sid referenced 1.91G - export/sid compressratio 1.69x - export/sid reservation none default export/sid volsize 5G local export/sid volblocksize 8K - export/sid checksum on default export/sid compression on inherited from export export/sid readonly off default export/sid copies 1 default export/sid refreservation 5.16G local export/sid primarycache all default export/sid secondarycache all default export/sid usedbysnapshots 0 - export/sid usedbydataset 1.91G - export/sid usedbychildren 0 - export/sid usedbyrefreservation 3.25G - export/sid logbias latency default export/sid dedup off default export/sid mlslabel none default export/sid sync standard default export/sid refcompressratio 1.69x - export/sid written 1.91G - Note that this zvol has compression enabled - this would be a good choice for a mail server's storage disk - mail is highly compressible. depending on available RAM in the server and the kind of mail typically received (e.g. multiple copies of the same email), de-duping the zvol may also be worthwhile. > > Any suggestions? > > I would aim to run ZFS in the mail domU, and treat the zvol as a > "logical volume" block device. You will have some overhead from the > double checksums, but robust performance. It treats the underlying > dom0 ZFS as a fancy LVM, essentially. You probably also need to > allocate substantially more memory to the domU than you would > otherwise. That's really not needed. Most VMs just need fast, reliable storage, and know or care exactly what the underlyingstorage is (nor should they have to) - it's abstracted away as a virtio disk, /dev/vda or /dev/vdb or as an iscsi disk. There may be some exceptions where the VM needs to run ZFS itself on a bunch of zvols, but the only real use-case i've found is for experimenting with and testing zfs itself (e.g. i've created numerous zvols of a few hundred MB each and used them in a VM to create a zpool from them) being able to snapshot and zfs send within the VM itself could be useful. OTOH rsync provides a similar incremental backup. craig -- craig sanders <cas(a)taz.net.au>

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bad ext3 filesystem
by James Harper 31 Oct '12

31 Oct '12

I have an unusual situation with an ext3 filesystem on a Xen DomU. I get the following on boot: [ 18.153177] blkfront: barrier: empty write xvda1 op failed [ 18.153195] blkfront: xvda1: barrier or flush: disabled [ 18.153206] end_request: I/O error, dev xvda1, sector 20975896 [ 18.153214] end_request: I/O error, dev xvda1, sector 20975896 [ 18.153222] Buffer I/O error on device xvda1, logical block 2621987 [ 18.153229] lost page write due to I/O error on xvda1 [ 18.153253] Aborting journal on device xvda1. [ ok ] Cleaning up temporary files.... [ 19.041362] EXT3-fs (xvda1): error: ext3_journal_start_sb: Detected aborted journal [ 19.041382] EXT3-fs (xvda1): error: remounting filesystem read-only The sequence of events that lead to this was: 1. Filesystem ran out of space (debugging options on for something I was testing and it filled up within hours) 2. Stopped the VM 3. resize2fs 4. Started VM e2fsck in Dom0 on the VM's filesystem (while the VM isn't running!!) shows no problems. I've tried removing and re-creating the journal. The underlying block device was resized from 10G to 20G, so sector 20975896 is well within the bounds of the disk. Should I cut my losses and create a new fs and copy all the files over or can someone suggest a fix? (FYI, the sequence of events in the logs above is the DomU trying to establish if the underlying vbd interface supports barriers, which it appears to not) Thanks James

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Is X vulnerable? - xinput and lack of app level isolation.
by Julian 31 Oct '12

31 Oct '12

Hi, Typing this email now in thunderbird, and watching every single keystroke being logged from an open X terminal. How could I not known about this? I've only ever played with xev but the application window must have a least some focus (sloppy for mouse, selected for keyboard). Not only is xinput more useful than xev, but also more revealing to how vulnerable X can be to ones favorite and "trusted" X applications. I came across this while browsing unanswered questions in unix.stackexchange.com. (can't find it right now). Surely this is not true; "Any X window application can log all device inputs regardless of what X window application has focus" But thats not all that is possible. Anyhow I had to try it out for myself... > apt-get install xinput > xinput list > xinput test <id of device> Xinput logs absolutely everything, anywhere. Regardless. Even an X application that opens as a different user (xauth). Do I trust any and all of the x applications I run? Thanks for the software, but I don't sorry. I'm not impressed by this at all and I'm ashamed I never new about it. I honestly thought there was some level of isolation, but there appears to be none. http://theinvisiblethings.blogspot.com.au/2011/04/linux-security-circus-on-… A rather heavy alternative using xen virtualisation (apps run in different "zones") http://qubes-os.org Remember this has nothing to do with xauth or xhost. This is a feature of a single displayed instance of X. Login to your bank, paypal, su as root, whatever and hope xeyes isn't logging your keystokes or run xinput and watch it for yourself. Something to think about. Regards, Julian.

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Mailman question
by Chris Samuel 30 Oct '12

30 Oct '12

Hi folks, If you've got a (very low traffic) Mailman list and it's been set up with digests and has subscribers who've enabled digests, what happens to them if you should disable digests? My guess is that they'll get emails as per normal from then on (or at least I would hope they would), but has anyone got experience with it? This is Mailman from Debian Stable: mailman: Installed: 1:2.1.13-5 Candidate: 1:2.1.13-5 Version table: *** 1:2.1.13-5 0 500 http://mirror.aarnet.edu.au/pub/debian/ squeeze/main i386 Packages 500 http://security.debian.org/ squeeze/updates/main i386 Packages 100 /var/lib/dpkg/status cheers! Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC

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CodeWeavers CrossOver free tomorrow
by Sean Crosby 30 Oct '12

30 Oct '12

For those who may be interested. CodeWeavers CrossOver is free from 4pm AEDST tomorrow for 24hrs - http://flock.codeweavers.com/ I use it for Microsoft Office (especially Excel), but I've also run games in it with great success Sean

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Compressing images in PDF files
by Jason White 25 Oct '12

25 Oct '12

How can I most effectively compress scanned page images in PDF files without unduly degrading the visual quality? I've been trying it with ImageMagick and a file that I want to compress, but so far without achieving much compression. The ImageMagick identify command, applied to one of the original pages shows: PDF 595x842 595x842+0+0 16-bit Bilevel DirectClass 63.2KB 0.000u 0:00.009 I've been experimenting a little with the -compress, -density and -quality commands of the convert command, but without as much progress as I would prefer. In most cases the output is larger than the input.

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gentoo Xorg: NVIDIA could not open the device file /dev/nividia0
by brettawiggins＠tpg.com.au 23 Oct '12

23 Oct '12

Hi Everyone, I'm having some problems getting Xorg working on my gentoo install. I've started a thread on the gentoo forums, I haven't received any replies since Friday. the link is located here; https://forums.gentoo.org/viewtopic-t-939876.html Basically I have been following the gentoo handbook; http://www.gentoo.org/doc/en/handbook/handbook-amd64.xml the Xorg guide; http://www.gentoo.org/doc/en/xorg-config.xml and the NVIDIA guide; http://www.gentoo.org/doc/en/nvidia-guide.xml When I type 'startx' after installing and configuring everything to use the NVIDIA binary blob (using both root and my normal user) I get the following output NVIDIA: could not open the device file /dev/nvidia0 (input/output error) Fatal server error: no screens found. This is not the first gentoo install I have done. But it is the first one where I have come across this error. My Xorg.0.log is located below; http://bpaste.net/show/51733/ /var/log/messages; http://bpaste.net/show/51739/ ANd finally my /etc/X11/xorg.conf; http://bpaste.net/show/51732/ I have tried everything that was suggested on the forums but still no dice. >From the log files it seems that the Xorg server is having trouble opening the device file /dev/nvidia0.. I could be wrong though.. Any help would be appreciated. Brett.

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Books for LUV library or free to a good home.
by Andrew Greig 22 Oct '12

22 Oct '12

Hi, I have "Running Linux" Fourth Edition and "Linux System Administration" 2001 which I no longer need, both are in good condition, I am moving home so my options are: 1 LUV library 2 Free to a good home 3 In the bin I am happy to bear the cost of postage. Andrew Greig

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Books for LUV library or free to a good home.
by Andrew Greig 21 Oct '12

21 Oct '12

Hi, I have "Running Linux" Fourth Edition and "Linux System Administration" 2001 which I no longer need, both are in good condition, I am moving home so my options are: 1 LUV library 2 Free to a good home 3 In the bin I am happy to bear the cost of postage. Andrew Greig

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