> 2. Are the RAM requirements for ZFS with dedup based on the total > available zpool size (I'm not using thin provisioning), or just on how > much data is in the filesystem being deduped? That is, if I have 500 > GB of deduped data but 6 TB of possible storage, which number is > relevant for calculating RAM requirements?
It's based on the data stored in the zpool. You'll need about 200 bytes of per DDT (data deduplication table) entry, meaning about 1,2GB per 1TB stored on 128kB blocks. With smaller blocks (smaller files are stored in smaller blocks), that means more memory. With only large files, 1,2GB or 1,5GB per 1TB stored data should sufffice. > 3. What are the RAM requirements for ZFS in the absence of dedup? That > is, if I only have deduped filesystems in an exported state, and all > that is active is non-deduped, is 4 GB enough? Probably not, see above. > 4. How does the L2ARC come into play? I can afford to buy a fast Intel > X25M G2, for instance, or any of the newer SandForce-based MLC SSDs to > cache the dedup table. But does it work that way? It's not really > affordable for me to get more than 16 GB of RAM on this system, > because there are only four slots available, and the 8 GB DIMMS are a > bit pricey. L2ARC will buffer the DDT along with the data, so if you get some good SSDs (such as Crucial RealSSD C300), this will speed things up quite a bit. > 5. Could I use one of the PCIe-based SSD cards for this purpose, such > as the brand-new OCZ Revo? That should be somewhere between a > SATA-based SSD and RAM. If your budget is low, as it may seem, good SATA SSDs will probably be the best. They can help out quite a bit. Just remember that dedup on opensolaris is not thoroughly tested yet. It works, but AFAIK there are still issues with long hangs in case of unexpected reboots. Disclaimer: I'm not an Oracle (nor Sun) employee - this is just my advice to you based on testing dedup on my test systems. 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
