Administrator’s Command Line Guide
Table Of Contents
- Introduction
- Accessing Acronis Storage Clusters via iSCSI
- Preparing to Work with Acronis Storage iSCSI Targets
- Creating and Running Acronis Storage iSCSI Targets
- Listing Acronis Storage iSCSI Targets
- Transferring Acronis Storage iSCSI Targets Between Acronis Storage Nodes
- Stopping Acronis Storage iSCSI Targets
- Deleting Acronis Storage iSCSI Targets
- Configuring Multipath I/O for Acronis Storage iSCSI Targets
- Managing CHAP Accounts for Acronis Storage iSCSI Targets
- Managing LUN Snapshots
- Accessing Acronis Storage Clusters via S3 Protocol
- Monitoring Acronis Storage Clusters
- Managing Cluster Security
- Maximizing Cluster Performance
6.5. Improving High-Capacity HDD Performance
issues an unaligned write request, the HDD has to align the beginning and end of that request to 4KB bound-
aries. To do this, the HDD reads the request’s head and tail ranges to determine an even number of sectors
to modify. For example, on a request to write a 4KB block at a 2KB offset, HDD will read the 0-2KB and 6-8KB
ranges to modify the entire 0-8KB data range.
The typical reasons of poor performance with 4KB sector HDDs are:
1. Host OS file system unaligned on the 4KB boundary. The make-cs command of Acronis Storage tries to
detect and report such issues to the administrator in advance, but be aware that the fdisk utility is not
recommended for partitioning HDDs. You should use parted instead.
2. Unaligned writes (e.g., 1KB) performed by guest OS. Many legacy operating systems, like Microsoft Win-
dows XP and Windows Server 2003 or Red Hat Enterprise Linux 5.x, have unaligned partitions by default
and generate unaligned I/O patterns which are quite slow on both Acronis Storage and actual HDDs with
4KB sectors. If you plan running such legacy operating systems, consider the following:
• Using smaller HDDs with 512-byte sectors, or use SSD journaling for CS services which mitigates the
issue to some extent.
• Aligning OS partitions properly.
You can check for unaligned write operations in the cluster by as follows:
1. Run the vstorage top or stat command. For example:
# vstorage -c stor1 top
2. Press i to display the RMW and JRMW columns in the CS part of the top output.
3. Check the RMW or JRMW counters, which are explained below.
• When SSD journaling is used, the RMW counter shows the number of requests which lead to Read-
Modify-Write cycles, while the JRMW counter shows the number of Read-Modify-Write cycles miti-
gated by the use of SSD journals.
• When SSD journaling is not used, the JRMW counter shows the number of unaligned requests which
potentially generate Read-Modify-Write cycles on the HDD in question.
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