Two ZFS pools on one system: load on one pool badly affects other one

[Lev Serebryakov]

 I have system with two ZFS pools. Both pools are RADIZ on HDDs (not SSDs), and don't share any storage hardware. One pool is "my private space" and other one is storage for torrents.

 Private space contains mirrors of FreeBSD SVN, my home directory, etc. Storage for torrents contains torrents.

 My home directory contains, among other data, working copies of FreeBSD src and ports.

 When torrent-client is stopped, disk-depended operations on PRIVATE pool like "svn up ~/FreeBSD/ports" starts immediately on cold caches.

 When torrent-client are running (and reads about 5-6MB/s in small chunks), "svn up ~/FreeBSD/ports" could wait up to 5 minutes before start output of updated paths. ^T shows this:

load: 0.48  cmd: svn 18126 [zio->io_cv] 275.95r 3.14u 6.14s 2% 21388k

 Is it normal? I understand, that ARC is shared between pools, but it looks like too much interaction: there are NO shared I/O resources (disks, controllers) between pools and these operations, but "svn" waits 60-300 seconds for some condition variable!

-- 
// Lev Serebryakov

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