Ok, replying with the details of what I've found so far. First of all, SSD devices, despite high published IOPS figures hide very poor IOPS *write* figures. I've been sent the manual for the Mtron Pro 7000 series SSD's, and while they have random read figures in the 12,000 range, the random write figures are just 130. http://www.diamondpoint.co.uk/manuals/storage/mtron/MSP-SATA7025.pdf
The exception to that rule appears to be the STEC Zeus IOPS. That little beauty can handle 18,000 IOPS writing (52,000 reading). Unfortunately the 18GB model costs £9,280. http://www.stec-inc.com/downloads/flash_datasheets/iopsdatasheet.pdf The Gigabyte iRAM looks great. £100 for the basic unit, around £200 fully populated with 4GB. That may be a tad low capacity, but for just the ZIL it should be plenty. However, the PCI model is out due to it's 5v requirement, leaving just the 5.25" form factor device. That will probably work, and it's reasonably cheap, but I'm not overly happy about plugging a Y splitter into the motherboard power socket. http://www.gigabyte.com.tw/Products/Storage/Products_Overview.aspx?ProductID=2678 There's also the HyperOs HyperDrive 4. Again a SATA memory device, this fits in a 5.25" bay and supports up to 8x 2GB DDR chips, giving 16GB of storage capable of 35,000 IOPS. It's a tad pricey though, around £1,700 for a populated 16GB model. On the plus side, it has the option to save to a laptop drive or compact flash card in the event of a power cut. http://www.hyperossystems.co.uk/ However, all of these devices rely on the SATA interface, and while that's tried & tested, you're limited to around 120MB/s throughput. Fine if you're running over gigabit, but that could be a limitation over Infiniband. With that in mind, I've been looking at PCI-e based solutions. These are very thin on the ground, but there are a couple around if you hunt: VMetro (previously Micro Memory) look very good. They have a 2GB PCI-e device, quoting throughput figures of 521MB/s and IOPS of 6.7 million. Unfortunately Vmetro don't seem to want to sell to the general public so I'm not holding my breath on being able to get hold of one of these. http://www.vmetro.com/category4304.html The best option for performance would appear to be the Fusion ioDrive, being launched right now. It's a PCI-e SSD device, supporting 600MB/s writes, and a quoted 100,000 IOPS. Pricing should be around £1,200 for the 80GB model, which is a little pricey when compared to the iRAM, but for 20x the capacity it's pretty reasonable. http://www.fusionio.com/products.aspx The downside is that it appears the ioDrive is being launched with Linux drivers only. Windows drivers will apparently follow in 3 months, and I have no idea how long it may be for Solaris. Summary ======== With the ioDrive not a viable option yet, the iRAM appears to the best in terms of price/performance. However that 5v problem I mentioned earlier turns into a major headache. It means the 5.25" form factor is the only one possible in a modern server. For me, that in turn means I can't use the Supermicro 836TQ chassis with it's 16 hot swop SATA bays. Instead, the best alternative I've found is a Chenbro RM 313. That has six 5.25" bays which means I can fit two Supermicro's 8x 2.5" SATA trays in four of them, and iRAM's in the remaining two. That gives me a pair of i-RAM's for the ZIL plus my original 16 hot swop drive bays. Unfortunately, my drives are now 2.5" devices instead of 3.5" and that has yet another knock on effect on the price. Ultimately I wind up with a server that's a full 50% more expensive (£2,700 instead of £1,800), has 2/3 of the capacity, and is limited to 120MB/s write throughput instead of nearer 840MB/s. When you put it like that, the i-RAM doesn't sound like such a bargain any more. For now I think I'll go without any type of nvram cache. But there is light at the end of the tunnel. We'll be keeping an eye on the Fusion Drive since that looks very promising, and it also appears there's a good chance of Sun getting in on the game: Jonathan Schwartz is writing about this very stuff right now: http://blogs.sun.com/jonathan/entry/not_a_flash_in_the This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
