[PVE-User] openiscsi with Proxmox

Pongrácz István pongracz.istvan at gmail.com
Thu Jan 2 20:31:34 CET 2014

----------------eredeti üzenet-----------------
Feladó: "Fábio Rabelo" fabio at fabiorabelo.wiki.br 
Címzett: "Muhammad Yousuf Khan" sirtcp at gmail.com , pve-user at pve.proxmox.com 
Dátum: Thu, 2 Jan 2014 16:10:28 -0200
> I am not an expert on ZFS, the best place to ask anything is the
> OmniOS forum ...
> But that something I can say, RAM memory !
> The people who give me help when I was implementing says this :
> 16GB of RAM for boot, PLUS 1 GB of RAM for each 1TB os raw disk space !
> And one more thing, the Sata ports in your system are 3 GB/s or 6 GB/s ?
> It makes a lot of difference,
> mainly in the SSD ZIL/L2ARK disks ...


Some corrections:

Yes, it is true, more ram is better, but not as strictly as you wrote and these rule of thumbs seems for dedup, which is not really recommended for non-experts.

Terms (very very basic mode, google for the details):

ARC - memory cache, used or contains metadata, raw data, l2arc metadata - it is located in the RAM, depends on the implementation (solaris, *bsd, linux), it is safe to limit to your phisycal ram/2

L2ARC - aka ssd cache - size matters, but effects to ARC size (of course, you need to store metadata of l2arc somewhere) - it contains hot raw data (not file, but regions)

ZIL - for sync writes - always has ZIL on the pools (never bigger than part of your memory, because ZIL never used for read, but if the system crashed deadly -> next reboot the system first recovers the pending sync writes to the pool)

SLOG - dedicated device (partition) to hold ZIL on it instead of the pool (much quicker than pool -> high iops for sync writes)

You should know your typical workload, goals and spend some time to figure out, how to tune the system for your needs.

Please note, of course ZFS has overhead, because the main purpose to keep your data as safe as possible. I do not want to start a filesystem war, but at this moment ZFS is the only filesystem which has such a great features and can keep your data really safe. No other solutions can provide the same. Anyway, always use backup :)

I had problems with lvm2 snapshot, nightly backups, save the backup somewhere, replicate, hardware raid issues, drbd fatal error etc. when I used them with Proxmox in the last years.

My opinion, proxmox is much better with native ZFS thank the existing local options, including live snapshot(s), backup, tuning (like compression) etc.

So, start playing with ZFS :)

(StartIT Kft., Hungary)

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