Lew Wolfgang wrote:
On 02/10/2013 12:43 PM, Dennis Gallien wrote:
Advice, please . . .
The default filesystem reserved blocks is 5%. IIRC that goes back a long time to when much smaller drives were in use. Is there a formula or rule-of-thumb now for today's large drives/partitions? I have quite a few 100-300GB partitions which I have tuned down to 3%, but it still seems I'm wasting a lot of space. Suggestions?
Hi Dennis,
As I recall, the reserved blocks were used to improve read/write performance because it makes it easier to find contiguous blocks. Anton Aylward wrote: Certainly not ones that use B-Tree algorithms!
----- Sorry to bring this up so long after the fact, but I wanted to add some *counter* information to the idea of *decreasing* a reserve factor. Instead of decreasing it, there are times when you might want to increase it -- it depends on *your priorities*. If you need space and don't care so much about speed, shrinking is likely the best way to go, but if you want to keep your disks running in their maximum speed range, I've noticed with 1-1.5TB partitions on a 24gB (12x2tB) RAID that free space should be kept around 20-25% and that's on a B-Tree based file system (XFS). That's because my max rate in read/write is 1TB/s, so even the smallest delays will create a much more noticeable hit in performance than they would out of 1 disk -- i.e. the computer can do many computations while the I/O controller is doing a 64K read/write on 1 disk, but the time it has to do calculations on a 12 spindle raid is a decimal order of magnitude less. So the cpu needs to search through 12X the data in 1/10th the time to maintain max I/O rates. The block allocator starts having problems finding large contiguous free spaces on file systems over 75% full, if (like me) you've gone up into the low 90's% usage, and back down. Once you've done that, you've got files spread throughout the free area. (I could rebuild the fs from scratch and that would give some more speed, until I let it get too full again). If your HD was the speed of a floppy, using it up 99%, you wouldn't notice a speed hit because the I/O was so slow, but the faster your HD subsystem, the more you'll notice the lag time caused by the block allocator and the buffering system. Many people with RAIDs have noticed a 30% or greater speed boost by avoiding the buffer cache. As long as CPU and memory speeds were staying 100-1000 times faster than disk, alot can be done to optimize I/O in memory, but with cpu speeds going down (to conserve power) and disk speeds going up with moves to SSD's and RAID's, those same algorithms won't work as well at the limits... -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org