Date: Mon, 4 Mar 2024 08:19:49 +0100 From: Andrea Venturoli <ml@netfence.it> To: freebsd-questions@freebsd.org Subject: ZFS ARC memory requirements Message-ID: <7f7a9f1f-8a2b-41ef-a6a7-1dc1e2f160af@netfence.it>
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Hello. I'm planning a machine to be used (almost) only as a backup host. It will have a "system" SSD-based ZFS pool (possibly 1TB mirror) for OS and programs and a large dedicated HDD-based ZRAID1 for backups (initially 160-200 TB, but may grow in the future). I read the rule of thumbs for RAM is 1GB per TB of storage, which would possibly mean 192GiB!!!, but I also read this is argued upon. Considering that: _ backup data will be organized in "volumes", so I'll have about ~2000 files totally on the backup pool; _ i do not plan to use deduplication and I'll probably disable compression (since most of the data to be backed up is uncompressible and the backup software already tries that anyway); _ snapshots make very little sense on such a pool (altough I'll use them heavily on the "system" pool, but that's small); _ daily throughput will be probably limited by the network or the clients, altough I plan to do monthly "consolidation" of backups and periodical disk to tape copies; _ it's very unlikely data (not metadata) will be read more than once in a row, so I don't think it will benefit from caching; my guess would be that I don't need that much RAM and 64 or even 32GiB would be enough. Opinions? bye & Thanks av.
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