[OpenIndiana-discuss] ashift 13?

[Jason Matthews]

On 4/7/2015 11:07 AM, Jim Klimov wrote:
>
> As for inflation - whenever you have smaller zfs allocations, such as those "tails" from blocks sized not power of 2 thanks to compression, they become a complete minimal "recordsize" block such as 4k or 8k as native to your drives, with trailing zero-padding. Some metadata blocks may also fall into this category, though for larger files these are clustered at 16kb(?) chunks. You also have less uberblocks in the fixed-size ring buffer of zpool labels.

I am not sure tails justifies the inflation. I can accept some increased 
utilization from tails but this is totally out of line.

Here is a 512b system of a database master.
root at shard035a:/home/postgres/data/base/16414# du -hs .
  203G   .
root at shard035a:/home/postgres/data/base/16414# ls -l |wc -l
     4109

203GB and 4109 files.

Here is the slave that I built from the master yesterday. They should be 
nearly identical.

root at shard035b:/home/postgres/data/base/16414# du -hs .
  474G   .
root at shard035b:/home/postgres/data/base/16414# ls -l |wc -l
     4081

My feeling is there are not enough tails in 4100 files to consume 271GB 
of storage. I dont understand what is going on just yet.

j.




> On the upside, if your ssd does compression, these zeroes will in effect likely count toward wear-leveling reserves ;) With hdds this is more of a lost space as compared to 512-byte sectored disks. However this just become similar to usage on other systems (ext3, ntfs) typically with 4k clusters anyway. So we're told to not worry and love the a-bomb ;)
>