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68 lines
2.7 KiB
Plaintext
68 lines
2.7 KiB
Plaintext
SCST Performance
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================
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A question that is asked often is how to tune performance. This means how to
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improve the IOPS and/or bandwidth measured at the initiator side. In this
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README it is explained how to optimize storage performance.
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Local storage
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-------------
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Start with measuring the performance of the local block device(s). IOPS can be
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measured e.g. as follows:
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fio --ioengine=libaio --rw=randread --ioscheduler=none --numjobs=$(nproc) \
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--runtime=60 --group_reporting=1 --gtod_reduce=1 --norandommap \
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--thread --buffered=0 --iodepth=256 --iodepth_batch=128 --bs=4k \
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--name=bdev --filename=/dev/...
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The bandwidth supported by a block device can be measured by increasing the
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block size to a larger value in the above command, e.g. --bs=1M.
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Storage network
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---------------
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Start with measuring the network bandwidth using your favorite tool, e.g.
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netperf for non-RDMA networks or ib_write_bw for RDMA networks.
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Next, add a nullio LUN to SCST, e.g. by adding the following in /etc/scst.conf:
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HANDLER vdisk_nullio {
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DEVICE disk09 {
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blocksize 4096
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size_mb 256
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}
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}
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TARGET_DRIVER ... {
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TARGET ... {
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LUN ... disk09
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}
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}
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After a nullio LUN has been added, verify that this LUN is visible at the
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initiator side. If it is not visible at the initiator side, consider
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rescanning LUNs or disconnecting and reconnecting the initiator system to the
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SCST server.
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Once the nullio LUN is visible at the initiator side, measure IOPS and
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bandwidth. The bandwidth should be close to the network bandwidth. When using
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the Linux iSCSI initiator this may require configuring multiple iSCSI sessions
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and activating multipathd on top of the multiple iSCSI sessions. The sequence
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for logging in with iSCSI and activating multiple iSCSI sessions is as follows:
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iscsiadm -m iface -I iface2 -o new
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iscsiadm -m iface -I iface2 -o update -n iface.initiatorname -v ${iqn2}
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iscsiadm -m discovery -t st -p ${scst_ip_address}
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iscsiadm -m discovery -t st -p ${scst_ip_address} -I iface2
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iscsiadm -m node -p ${scst_ip_address} -l
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iscsiadm -m node -p ${scst_ip_address} -I iface2 -l
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SCST Configuration
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------------------
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If the number of IOPS measured at the initiator side is significantly lower
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than the minimum of the IOPS supported by the local storage and the storage
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network, further tuning is required. Look up in /proc/interrupts which CPU
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cores process the most network and storage interrupts and configure the SCST
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kernel threads such that these run on other CPU cores than those that process
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the most interrupts by configuring the cpu_mask attribute. More information
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about the SCST cpu_mask sysfs attribute is available in the SCST README.
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