The ZIL is a write-only log that is only read after a power failure. Several GB is large enough for most workloads.
You can't use the Intel X25-E because it has a 32 or 64 MB volatile cache that can't be disabled neither flushed by ZFS. Imagine your server has a power failure while writing data to the pool. In normal situation, with ZIL on a reliable device, ZFS will read the ZIL and come back to a stable state at reboot. You may have lost some data (30 seconds) but the zpool works. With the Intel X25-E as ZIL some log data has been lost with the power failure (32/64MB max) which lead to a corrupted log and so ... you loose your zpool and all your data !! For the ZIL you need 2 reliable mirrored SSD devices with a supercapacitor that can flush the write cache to NAND when a power failure occurs. A hard-disk has a write cache but it can be disabled or flush by the operating system. For more informations : http://www.c0t0d0s0.org/archives/5993-Somewhat-stable-Solid-State.html -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
