I'm putting together a new server, based on a Dell PowerEdge T410. I have simple SAS controller, with six 2TB Hitachi DeskStar 7200 RPM SATA drives. The processor is a quad-core 2 GHz Core i7-based Xeon.
I will run the drives as one set of three mirror pairs striped together, for 6 TB of homogeneous storage. I'd like to run Dedup, but right now the server has only 4 GB of RAM. It has been pointed out to me several times that this is far too little. So how much should I buy? A few considerations: 1. I would like to run dedup on old copies of backups (dedup ratio for these filesystems are 3+). Basically I have a few years of backups onto tape, and will consolidate these. I need to have the data there on disk, but I rarely need to access it (maybe once a month). So those filesystems can be exported, and effectively shut off. Am I correct in guessing that, if a filesystem has been exported, its dedup table is not in RAM, and therefore is not relevant to RAM requirements? I don't mind if it's really slow to do the first and only copy to the file system, as I can let it run for a week without a problem. 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? 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? 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. 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. Thanks in advance for all of your advice and help. -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
