If I look at my disk utilization, in System Monitor under Gnome, I see File System details which lists Total, Free, Available and Used. The simple arithmetic works for Total, Free and Used, however in my case ‘Available’ is 12 GB less than ‘Free’.
Which unprincipled rogue stole 12 GB of my disk? Why, that’s almost an armful; I want it back! Where did it go?
On Wed, 2009-08-19 at 20:26 +0000, XEyedBear wrote:
> If I look at my disk utilization, in System Monitor under Gnome, I see
> File System details which lists Total, Free, Available and Used. The
> simple arithmetic works for Total, Free and Used, however in my case
> ‘Available’ is 12 GB less than ‘Free’.
>
> Which unprincipled rogue stole 12 GB of my disk? Why, that’s almost an
> armful; I want it back! Where did it go?
Two places. Likely this could be the minspace allocation for the root
user. It’s often set too high… shoot even at 1% that can be a huge
amount of space given today’s drives. That’s likely the cause.
The other possible place would be loss due to journal size, but that’s
usually not so large. Journaling can be a huge loss on SMALL
filesystems (e.g. <100M).
I could be wrong on what is actually causing the 12GB of missing space.
Maybe someone else can chime in.
Would this ‘minspace’ allocation apply to my system, where the disk in question contains only /SWAP and /home; the ‘system’ is on another hard drive?
To begin with, cjcox is talking about file systems (on partitions), like you did in your first post. So we are talking here about two partitions (and not about a disk).
One has swap (not /SWAP, it is not mounted). I do not think your observation is about this one.
Then the partition which is mounted on /home. I would prefer a little bit of freeway for root here. It is always convenient, when a user fills up the whole partition, if root can copy some files there to save them while he is redressing the problem. But as cjcox said, this is a percentage and that tends to be a bit to much nowadays with a default of 5% with ext3 on a multi Gb partition. It depends on the type of file system. When you have an ext3 one then look at
man tune2fs
(valid for ext2 AND ext3). Read about what the -m option can do for you.
I have now read about this option. At the default setting of 5% it would appear that about 12GB of disk space is being reserved. This appears to be far in excess of what I could possibly need. But, try as I might, I cannot seem to get this command to accept any of my inputs, now matter how I specify them. Having tried many , many ways, over the last 10 days, of specifying ‘2%’. none of which appear to be accepted, I have to accept the loss of 12 GB of my disk.
Seems a bit extravagant but it’s beyond my ability to change it.
Do those ways include just a plain 2, as in -m 2?
Not a good idea.
Most filesystems act a lot like hash tables. This has a great speed advantage compared to any other way of allocating space.
However when the filesystems get close to full, they get slow due to hash collisions that need to be resolved.
This is most easily taken care of by assuring that a percentage of the disk - say, 5% - is NOT used by in effect making it unavailable except for root. This isn’t space actually used by any data at all, you simply cannot fill the filesystem more than that without slowing I/O down badly.
Man, are you right. A couple of years ago, I performed some actions to regain this kind of lost diskspace, because I thought I would win around 40 GB, which I thought I needed. The results were dramatic. My mean main machine changed from a sportscar to a tractor. Since I had immediately filled the new available space, it was quite a job to revert to the old values. Bought an extra 250GB disk, added it to the machine, partitioned it with Yast, all in half an hour, space trouble gone.
After this experience I learned that every filesystem needs this ‘free’ space.
If the available 228 GB is nearly all used, it seems more storage will be needed soon. I don’t think gaining 7 or 8 GB will do much to alleviate that.
I will point out what no one else has mentioned so far, probably because it is well known to many of us. tune2fs cannot be used on a mounted drive to change the amount of reserved space. The disk has to be unmounted first.
That’s right, and not only for this.
While 12GB may seem like a lot, think in terms of the cost of your HD. You probably paid somewhere between $50 and $100 for it. That extra 3% only cost you between $1.50 to $3.00 over the lifetime of the HD. That’s a minuscule price to pay for performance. Besides, if you are down to your last 12GB, it’s time you got a new HD anyway.