Hello, When driving reads or writes to ZFS continuously to a commerical backend storage (42 disk array with hardware raid controller exposing disk via fiber channel interface), I see time frames during which no IO takes place when it should. Reading the underlying raw disk device does not present this problem.
The pauses begin after 3-4 minutes of IO have taken place, and then they appear after every 60 seconds. At that time the pauses last for about 3 seconds and IO resumes. The server itself does nothing else during these times. The server is a Dell 1950 with dual quad core CPUs with 32GB of RAM. I have performed the same tests on a second piece of identical hardware with the same results. I have included a link to a graph that depicts what I see at the fiber channel interface of the server: http://www3.amherst.edu/~swplotner/comstar/debug/zfs_pauses.png Here is one of the pauses shown with zpool iostat: vg_satabeast8_vol0 1004G 3.08T 3.09K 0 120M 0 vg_satabeast8_vol0 1004G 3.08T 3.09K 0 109M 0 vg_satabeast8_vol0 1004G 3.08T 3.00K 0 105M 0 vg_satabeast8_vol0 1004G 3.08T 3.02K 0 111M 0 vg_satabeast8_vol0 1004G 3.08T 3.25K 0 118M 0 vg_satabeast8_vol0 1004G 3.08T 3.17K 0 111M 0 vg_satabeast8_vol0 1004G 3.08T 2.34K 0 86.5M 0 vg_satabeast8_vol0 1004G 3.08T 3.19K 0 115M 0 vg_satabeast8_vol0 1004G 3.08T 2.24K 0 67.2M 0 vg_satabeast8_vol0 1004G 3.08T 0 0 0 0 <- these 3 lines are 1 pause in the graph (3 seconds worth) vg_satabeast8_vol0 1004G 3.08T 0 0 0 0 <- the graph shows 3 of those pauses. vg_satabeast8_vol0 1004G 3.08T 716 0 33.5M 0 <- vg_satabeast8_vol0 1004G 3.08T 3.36K 0 112M 0 vg_satabeast8_vol0 1004G 3.08T 4.14K 0 113M 0 vg_satabeast8_vol0 1004G 3.08T 3.82K 0 111M 0 vg_satabeast8_vol0 1004G 3.08T 2.09K 0 72.8M 0 vg_satabeast8_vol0 1004G 3.08T 3.27K 0 102M 0 vg_satabeast8_vol0 1004G 3.08T 2.88K 0 102M 0 vg_satabeast8_vol0 1004G 3.08T 3.14K 0 114M 0 vg_satabeast8_vol0 1004G 3.08T 2.65K 0 97.6M 0 vg_satabeast8_vol0 1004G 3.08T 2.93K 0 105M 0 The pauses are of concern - actually - they are a problem since no IO is being processed for several seconds each minute and if they could be removed could make zfs really fast. Steffen ________________________________________________________________________ _______________________ Steffen Plotner Amherst College Tel (413) 542-2348 Systems/Network Administrator/Programmer PO BOX 5000 Fax (413) 542-2626 Systems & Networking Amherst, MA 01002-5000 swplot...@amherst.edu
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