[ZFS] starving reads while idle disks

[Lytochkin Boris]

Hi.

> Do you see the same read-stravation when writing the tar to a file ? (possibly outside the zpool).
Yep.
> I have anecdotal suspicion that /dev/null has some performance hit of blocking or locking.
No-no. Every program that tries to read from ZFS faces this issue actually.

 I found something more interesting. Lets presume I have 10 big dirs in .
 Issuing tar|dd command on separate dirs (so spawning 10 "threads")
 simultaneously will result in 10x faster reads cumulatively (I saw
 15Mb/s in zpool iostat), and disk load may be as high as 70%.
 So I think there is some read throttling thing that limits read speed
 per read(). But still no clue where to find this bottleneck.

-- 
Wbr,
Boris.