Darren Reed wrote:
Solid state disk often has a higher failure rate than normal disk and a limited write cycle. Hence it is often desirable to try and redesign the filesystem to do fewer writes when it is on (for example) compact flash, so moving "hot blocks" to fast storage can have consequences.
Solid state storage does not necessarily mean flash. For example, I have recently performed some testing of Sun's Directory Server in conjunction with solid state disks from two different vendors. Both of these used standard DRAM, so there's no real limit to the number of writes that can be performed. They have lots of internal redundancy features (e.g., ECC memory with chipkill, redundant power supplies, internal UPSes, and internal hard drives to protect against extended power outages), but both vendors said that customers often use other forms of redundancy (e.g., mirror to traditional disk, or RAID across multiple solid-state devices).
One of the vendors mentioned that both SVM and VxVM have the ability to designate one disk in a mirror as "write only" (unless the other has failed) which can be good for providing redundancy with cheaper, traditional storage. All reads would still come from the solid state storage so they would be very fast, and as long as the write rate doesn't exceed that of the traditional disk then there wouldn't be much adverse performance impact from the slower disk in the mirror. I don't believe that ZFS has this capability, but it could be something worth looking into. The original suggestion provided in this thread would potentially work well in that kind of setup.
ZFS with compression can also provide a notable win because the compression can significantly reduce the amount of storage required, which can help cut down on the costs. Solid state disks like this are expensive (both of the 32GB disks that I tested list at around $60K), so controlling costs is important.
Neil _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
