file corruption solution (soft-update or ZFS)

Paul Kraus paul at
Sat May 25 15:45:00 UTC 2013

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

> On Thu, May 23, 2013 at 5:33 AM, Warren Block <wblock at> wrote:
>> ..
>> 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 that
> can be satisfied with dedicated cache devices (on SSD for performance and
> 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 adequate.

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

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