----- Original Message -----
> Thanks roy, I read a lot around and also was thinking it was a
> dedup-related problem. Although I did not find any indication of how
> many RAM is enough, and never find something saying "Do not use dedup,
> it will definitely crash your server". I'm using a Dell Xeon with 4 Gb
> of RAM, maybe it is not an uber-server but it works really well (when
> it is not hung, I mean).
> Do you have an idea about the optimal config to have 1,5T of available
> space in 10 datasets (5 deduped), and 10 rotating snapshots?
> Thanks
Erik Timble had a post on this today, pasted below. Look though that, but
seriously, with 4 gigs of RAM and no L2ARC, dedup is of no use
roy
Actually, I think the rule-of-thumb is 270 bytes/DDT entry. It's 200
bytes of ARC for every L2ARC entry.
DDT doesn't count for this ARC space usage
E.g.: I have 1TB of 4k files that are to be deduped, and it turns
out that I have about a 5:1 dedup ratio. I'd also like to see how much
ARC usage I eat up with a 160GB L2ARC.
(1) How many entries are there in the DDT:
1TB of 4k files means there are 2^30 files (about 1 billion).
However, at a 5:1 dedup ratio, I'm only actually storing
20% of that, so I have about 214 million blocks.
Thus, I need a DDT of about 270 * 214 million =~ 58GB in size
(2) My L2ARC is 160GB in size, but I'm using 58GB for the DDT. Thus,
I have 102GB free for use as a data cache.
102GB / 4k =~ 27 million blocks can be stored in the
remaining L2ARC space.
However, 26 million files takes up: 200 * 27 million =~
5.5GB of space in ARC
Thus, I'd better have at least 5.5GB of RAM allocated
solely for L2ARC reference pointers, and no other use.
--
Vennlige hilsener / Best regards
roy
--
Roy Sigurd Karlsbakk
(+47) 97542685
r...@karlsbakk.net
http://blogg.karlsbakk.net/
--
I all pedagogikk er det essensielt at pensum presenteres intelligibelt. Det er
et elementært imperativ for alle pedagoger å unngå eksessiv anvendelse av
idiomer med fremmed opprinnelse. I de fleste tilfeller eksisterer adekvate og
relevante synonymer på norsk.
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
