http://storagemojo.com Data storage info & analysis Sun, 20 May 2012 13:26:14 +0000 hourly 1 http://wordpress.org/?v=3.3.2 http://storagemojo.com/zfs-threat-or-menace-pt-ii/comment-page-1/#comment-206060 Donald Ragbirsingh Sun, 18 Oct 2009 02:08:13 +0000 http://storagemojo.com/?page_id=151#comment-206060 ZFS is being adopted in preference to VXFS at my company. We've found some issues that demonstrate how a better understanding of ZFS is critical. A particular application was creating and deleting files so fast that the HDS USP had terrible i/o problems on a few 400GB filesystems - the transfer was a paltry 300MB/s when it should have been at least 700MB/s. When we disabled the ZIL - we found the culprit and the i/o went up. This M8000 domain had four Emulex LP11002 cards and four fibre connections interleaving the PCIe bridges within a single IOU. Admittedly - yes - ZFS is an excellent choice, but further testing showed that locating the ZFS Intent Log to a SSD would have bypassed this issue. HDS (and other frames) don't like ZFS to dictate when they should flush their NVRAM caches - in fact - ZFS takes a sequential write and transforms it into a pure random write. On RAID5 and RAID6 storage which is typically assigned - these luns within the internal RAID group showed high latencies. Careful planning is required, in my case RAID10 was actually better. ZFS is being adopted in preference to VXFS at my company. We’ve found some issues that demonstrate how a better understanding of ZFS is critical. A particular application was creating and deleting files so fast that the HDS USP had terrible i/o problems on a few 400GB filesystems – the transfer was a paltry 300MB/s when it should have been at least 700MB/s. When we disabled the ZIL – we found the culprit and the i/o went up. This M8000 domain had four Emulex LP11002 cards and four fibre connections interleaving the PCIe bridges within a single IOU. Admittedly – yes – ZFS is an excellent choice, but further testing showed that locating the ZFS Intent Log to a SSD would have bypassed this issue. HDS (and other frames) don’t like ZFS to dictate when they should flush their NVRAM caches – in fact – ZFS takes a sequential write and transforms it into a pure random write. On RAID5 and RAID6 storage which is typically assigned – these luns within the internal RAID group showed high latencies. Careful planning is required, in my case RAID10 was actually better.

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