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Optimizing Linux Use On a USB Flash Drive?
Buckbeak writes "I like to carry my Linux systems around with me, on USB flash drives. Typically, SanDisk Cruzers or Kingston HyperX. I encrypt the root partition and boot off the USB stick. Sometimes, the performance leaves something to be desired. I want to be able to do an 'apt-get upgrade' or 'yum update' while surfing but the experience is sometimes painful. What can I do to maximize the performance of Linux while running off of a slow medium? I've turned on 'noatime' in the mount options and I don't use a swap partition. Is there any way to minimize drive I/O or batch it up more? Is there any easy way to run in memory and write everything out when I shut down? I've tried both EXT2 and EXT3 and it doesn't seem to make much difference. Any other suggestions?"
Get a swap partition so that you can free up some memory for disk cache, for one. Enable laptop mode too.
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Well, the sucky thing about USB is it requires an inordinate amount of CPU. Normally this isnt a worry, but if you're using a encrypted loopback.. well ouch.
One thing you could instead use is the SD card slot and a USB loader. If you choose a 8GB class 6 SD card, you could have plenty of room for whatever, and 6MB/s minimum speed. You're still going to take the CPU hit for encryption, but that is your choice. The big thing is to stay off the USB.
One thing I've found really, really helps is to use smaller programs et al. While the difference in how long it takes to start up gnome-terminal vs rxvt or nautilus vs pcmanfm is minimal on a normal/modern desktop or laptop, the difference is substantial on a cheap USB flash drive. There's plenty of lists for lightweight applications, window managers etc for linux around online. In fact, I'll often just stick with terminal applications (moc, for instance).
Another option, if you're booting on a box which has a good internet connection, is to ssh -X things over a network. Not only does this save a large amount of space, but I've found it's often faster to have a program like Firefox start on my snazzy box at home and ssh -X over than waiting for it to load off of my crappy usb drive.
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It might be that the poor performance occurs when you're on a computer that only has USB1 support. On Dells this was added later than you might expect.
You might find you got better performance if you were to use a CD to hold most of the static software and the USB for just your home directory.
I know a little bit about this because I am one of the developers for TurnKey Linux, a new opensource project which builds small installable live CDs (we're up to 9) optimized for various mostly server-related tasks. I've been investigating supporting live USB mode.
Your generic run-of-the-mill USB drive has about fourth-half the read/write performance of your hard drive nowadays (10-15MB/s). Since there are no moving parts (spinning platters), usually the seek times are very good.
There are several things you can do to optimize the performance of an operating system running live from a USB drive:
1) buy a faster USB drive: a good USB drive (e.g., Lexar JumpDrive) can have 2-3 times the performance of a generic.
2) Use a Linux distribution with a smaller footprint such as DSL (50MB) or Puppy Linux (standard edition is 68MB): the smaller the footprint, the less your drive has to read, the faster your system will load.
3) Try loading the operating system system into a ramdisk: many live USB distributions have the ability to load themselves into RAM. With some you have to add a cheatcode in the bootloader. Others do it by default if there is enough memory (usually not a problem with small distributions and modern computers).
4) Try turning on readahead: many distributions which are designed to run from a live CD or live USB have a feature that reads ahead various files important to the boot sequence sequentially. Whether or not this helps depends on the characteristics of the storage medium you are using, but you should investigate it.
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make sure you are on USB 2.0- interface can kill you.
Also did you check the faq-
No seriously:
http://www.linux-usb.org/FAQ.html#i5
especially the section on:
Q: What is max_sectors and how should I use it?
A:For USB Mass Storage devices (that is, devices which use the usb-storage driver) max_sectors controls the maximum amount of data that will be transferred to or from the device in a single command. As the name implies this transfer length is measured in sectors, where a sector is 512 bytes (that's a logical sector size, not necessarily the same as the size of a physical sector on the device). Thus for example, max_sectors = 240 means that a single command will not transfer more than 120 KB of data.
Most USB flash drives are very slow, and rely on heavy cacheing to make them usable. That doesn't help when you need to write large amounts of data (ie. in an apt-get update/install).
Some flash drives that advertise themselves as 10-15MiB/sec write capable peak out at only 1 or 2, and even less with small-block random I/O (since the erase-write cycle operates on relatively large blocks).
Several vendors make specialized flash drives that are somewhat more expensive (ie. 20-50% over average), but perform much better.
One is here: OCZ Turbo USB 2.0
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Try out different filesystems, NILFS seems to be optimized for FLASH usage.
Brtfs could also be worth a try.
use the "noop" IO/Scheduler with nilfs: /sys/block/sdX/queue/scheduler
echo noop >
Postmark benchs on an usb-stick (shameless copied from here:
ext3 (mount -o noatime,noadirtime, normale Partition, scheduler cfq): 49 Transactions/s
nilfs2 (Partition aligned 128k, scheduler noop, protection_period 10s): 588 Transactions/s
I have an old 10GB laptop drive inside of a very low profile USB enclosure and it runs like 35x faster than my USB drive or something absurd like that. It's a little more sensitive to bumps but it's not exactly expensive for 10GB drives. You can get a 6 pack of used one on ebay for about $3-7 each. Best of all, in a good enclosure, it still fits in your pocket.
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You might want to try replacing many programs as you can with busybox. It's versions of utilities are less complete than the standard gnu utilities, but they are all rolled into one binary, so most likely most of that binary will get cached in ram pretty early and stay there.
Also, for any packages you build you should try to use the -Os option for gcc, and perhaps even strip the binaries to remove unused symbols and debug info.
Building the system as though this was an embedded system with a small disk should be a win in most cases since fewer things have to go over the wire to load a file and more of the binaries can fit into cache.
The best thing to do is make a ram disk and use that as swap space.
So the OS can use part of the memory as swap, rather than memory, and when the part it is using as memory is full it can copy it to the part it is using as disk? (Except it won't, because if I recall correctly the RAM disk, along with disk buffers, are all dynamically assigned in memory, so when you need to swap there's nowhere to swap to.)
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Just to let you know, tmpfs ignores the device path, you can put whatever you want in it (and you aren't actually using /dev/ram* with that).
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Dave Jones recently posted elsewhere his notes for improving things on the eee900. Several of the steps focus on getting proper performance out of the flash, and so would also apply to booting from a USB thumb drive or other flash media. Here's what he had to say:
Program Intellivision!
Using encrypted swap is really easy on a modern Linux distribution. A random key is assigned to the swap partition on boot-up, so that after power-off, the data's almost as good as gone.
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There's quite a discrepancy over the speeds on flash drives. Cheap flash drives run USB 1.1 and the transfer rates are around 1 MB/sec. USB 2.0 drives range from slow 10 MB/sec to close to 40 MB/sec. The fastest drives will cost easily over $100. The size of the drive will slow the transfer rate also. 4 GB drives are faster than 8 GB and so on. Corsair GT drives have close to 35 MB/sec read speeds, write speeds are always dramatically slower. I've installed a bootable PBX in a Flash on a 4 GB Corsair USB flash drive with very acceptable performance for teaching purposes. I can see other LAMP bootable installations popping up. Each student can have their own server to configure and boot-up then take shut it down and take it home.
Puppy has also done a lot of optimizing for running on a USB stick, and it can handle encrypted partitions. Check it out: puppylinux.org