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Date:      Sat, 25 May 2013 11:44:59 -0400
From:      Paul Kraus <>
To:        Michael Sierchio <>
Cc:        saeedeh motlagh <>, freebsd-questions <>
Subject:   Re: file corruption solution (soft-update or ZFS)
Message-ID:  <>
In-Reply-To: <>
References:  <> <> <> <> <>

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On May 23, 2013, at 11:09 AM, Michael Sierchio <> =

> On Thu, May 23, 2013 at 5:33 AM, Warren Block <> =
>> ..
>> One thing mentioned earlier is that ZFS wants lots of memory.  4G-8G
>> minimum, some might say as much as the server will hold.
> Not necessarily so - deduplication places great demands on memory, but =
> can be satisfied with dedicated cache devices (on SSD for performance =
> safety reasons).  Without dedup, the requirements are more modest.

The rule of thumb for DeDupe is 1GB physical RAM for every 1TB of =
capacity. The issue is that the DeDupe metadata table must live in the =
ARC for good performance. The discussion I have seen on the ZFS lists =
indicates that L2ARC is not really adequate for this, so adding cache =
devices (SSD's) don't really help.

On the other hand, you can use ZFS without DeDupe with as little as 2GB =
of total system RAM (depending on what else the system is doing). In my =
experience, the amount of RAM depends on the amount of I/O not the =
amount of storage. I find between 1GB and 3GB space for the ARC is =

Paul Kraus
Deputy Technical Director, LoneStarCon 3
Sound Coordinator, Schenectady Light Opera Company

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