[PVE-User] openiscsi with Proxmox

Alexandre DERUMIER aderumier at odiso.com
Fri Jan 3 12:38:55 CET 2014


about l2arc, be carefull of your block size.

Because, each block need around 200 bytes of memory to be mapped in l2arc. So if you use 4K block size for example,

and you put 1TB of l2arc, you need (1073741824/4 * 0.2) = 54GB of memory.

----- Mail original ----- 

De: "Pongrácz István" <pongracz.istvan at gmail.com> 
À: "Muhammad Yousuf Khan" <sirtcp at gmail.com>, "pve-user pve.proxmox.com" <pve-user at pve.proxmox.com> 
Envoyé: Vendredi 3 Janvier 2014 12:27:22 
Objet: Re: [PVE-User] openiscsi with Proxmox 


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

first of thanks for writing an informative input. 
as it seems, a person must need 1 SSD for L2ARC and 2xmirrored SSDs for ZIL, now the question is do we also need a SSD for SLOG 

ZIL is the write cache in memory. SLOG is like a raid1 mirror to ZIL located on storage. This could be on dedicated SSD or in a partition on an SSD. In your case it could be enough to make some partitions on a reliable SSD and use it for system (ext3/4), L2ARC (10-100GB?), SLOG (1-2GB). Please remember, only sync writes goes to ZIL, in the worst case you lost 5 seconds of data if the SLOG device dies too. (no rule of thumb, you need to check your implementation details) 

Thanks Fabio, i have a dell workstation 490 and it only support SATAv2 or 3gb speed. 

do you guys think by tweaking ZFS a bit and using multiple SSDs for ZIL, L2ARC and may be SLOG can give me 4x1GB from each interface. as i mentioned i have 12GB RAM. 

No idea. You should play with the tunings (compression, raidz2/3). Too much variables (cpu throughput, your pool config, fragmentation of course - COW, IO direction). I have a AMD T56N system with 2 x sata port multiplicators with 6x 2.5" hitachi disks, I can achieve 50MB/sec write to them with no compression - video, but sometimes it droppes to 10-20MB/sec. 
So, you should test your system and monitor it. 

we are a small company, not too much reads and writes, we mostly checkin checkout our software codes to the VM repositories. 
so i think generally we have less IOPS but yes we have huge files in form of VMs and they should be backed up every week and snapshot ZFS on daily basis 

Raidz2/3 could be ok, depends on numbers of your disks. 

so with this load what you guys think, can i achieve 4x1gb Ethernet output? 


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