Hello all, I am thinking about a new laptop. I see that there are a number of higher-performance models (incidenatlly, they are also marketed as "gamer" ones) which offer two SATA 2.5" bays and an SD flash card slot. Vendors usually position the two-HDD bay part as either "get lots of capacity with RAID0 over two HDDs, or get some capacity and some performance by mixing one HDD with one SSD". Some vendors go as far as suggesting a highest performance with RAID0 over two SSDs.
Now, if I were to use this for work with ZFS on an OpenSolaris-descendant OS, and I like my data enough to want it mirrored, but still I want an SSD performance boost (i.e. to run VMs in real-time), I seem to have a number of options: 1) Use a ZFS mirror of two SSDs - seems too pricey 2) Use a HDD with redundant data (copies=2 or mirroring over two partitions), and an SSD for L2ARC (+maybe ZIL) - possible unreliability if the only HDD breaks 3) Use a ZFS mirror of two HDDs - lowest performance 4) Use a ZFS mirror of two HDDs and an SD card for L2ARC. Perhaps add another "built-in flash card" with PCMCIA adapters for CF, etc. Now, there is a couple of question points for me here. One was raised in my recent questions about CF ports in a Thumper. The general reply was that even high-performance CF cards are aimed for "linear" RW patterns and may be slower than HDDs for random access needed as L2ARCs, so flash cards may actually lower the system performance. I wonder if the same is the case with SD cards, and/or if anyone encountered (and can advise) some CF/SD cards with good random access performance (better than HDD random IOPS). Perhaps an extra IO path can be beneficial even if random performances are on the same scale - HDDs would have less work anyway and can perform better with their other tasks? On another hand, how would current ZFS behave if someone ejects an L2ARC device (flash card) and replaces it with another unsuspecting card, i.e. one from a photo camera? Would ZFS automatically replace the L2ARC device and kill the photos, or would the cache be disabled with no fatal implication for the pools nor for the other card? Ultimately, when the ex-L2ARC card gets plugged back in, would ZFS automagically attach it as the cache device, or does this have to be done manually? Second question regards single-HDD reliability: I can do ZFS mirroring over two partitions/slices, or I can configure "copies=2" for the datasets. Either way I think I can get protection from bad blocks of whatever nature, as long as the spindle spins. Can these two methods be considered equivalent, or is one preferred (and for what reason)? Also, how do other list readers place and solve their preferences with their OpenSolaris-based laptops? ;) Thanks, //Jim Klimov _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
