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Supermicro New Zealand
SAS Expander Direct Attached Storage
30 October 2008
The SAS Expander is akin to a switch of a Local Area Network but for Hard Disks. While we are unable to configure SAS Expanders for use as a Storage Area Network just yet, we can configure it as a glorified Direct Attached Storage. We explain how we do it with 3 examples.
Single Server with 3.5" HDDs
We can assume the server to be a 2U, 3U, 4U or 5U machine with plenty of space for installing hard disks. As SAS and SATA are point to point schemes, we must supply the same number of SAS or SATA channels as the number of hard disks. With a SAS Expander however, we can supply a lesser number of channels as the Expander will connect one channel to several hard disks like a switch. The diagram shows 16 HDDs in a hardware RAID configuration supported by a 4-channel SAS RAID control card. SAS has a bandwidth of 300MB/s and the performance degradation will be minimal for up to 4 HDDs per channel.
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Single Server with 2.5" HDDs
This scenario is similar to the first one except with the way we install the SAS Expander. In the first scenario, we install the Expander onto the back plane that allows the hard disks to be hot swapped and with status indication on the front panel. What do we do if we do not have an Expander? We can deploy a Supermicro Expander Caddy Set each supporting 8 hard disk drives of the 2.5" form factor. One such caddy set takes the space of 2x 5.25" bays only on a front panel. We can easily install 2 caddy sets for 16 hard disks supported by one 4-channel SAS RAID control card. The beauty of this arrangement is low latency because we have smaller HDD units and more spindles. It is most suitable for transactional processing. The diagram shows such caddy sets with an expander integrated
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External Storage
This is a more complex but powerful arrangement. In addition to whatever number of hard disks installed in the server, we can have an external chassis to accommodate more hard disks that can be set up through the same RAID controller card. The example below can be applied to 32 hard disks on a 4-channel RAID card. Note this calculation: 32 x 1.5TB = 48TB of raw data storage in a server! |
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or see http://www.compucon.co.nz/. Supermicro New Zealand is managed by Compucon.
-Editor
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Supermicro New Zealand
Managed by Compucon New Zealand
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