[CentOS] RAID 5 vs. RAID 10 -- product links ...

Mon Jul 25 12:19:28 UTC 2005
Bryan J. Smith <b.j.smith at ieee.org>

[ I assume you want to minimize costs -- e.g., 4 drives.  But I'll
include a full list of options regardless. ]

- Quality SATA RAID Cards ...

3Ware Escalade 8506-4LP/8/12 PCI64 (RAID-10 only, RAID-5 slow):  
[ 64-bit at 66MHz (0.5GBps), 64-bit ASIC, 2-4MB SRAM ]
  http://www.3ware.com/products/serial_ata8000.asp  

3Ware Escalade 9500S-4LP/8[MI]/12[MI]:  
[ 64-bit at 66MHz (0.5GBps), 64-bit ASIC, 2-4MB SRAM, 128+MB DRAM ]
  http://www.3ware.com/products/serial_ata9000.asp  

LSI Logic MegaRAID SATA 300-8X (8-channel SATA):  
[ 64-bit at 66-133MHz (0.5-1.0GBps), XScale IOP331, 128MB DRAM ] 
  http://www.lsilogic.com/products/megaraid/sata_300_8x.html  

- Quality U320 SCSI RAID Cards ...

LSI Logic MegaRAID SCSI 320-2X 2-channel U320 SCSI (PCI-X)
[ 64-bit at 66-133MHz (0.5-1.0GBps), XScale IOP321, 128+MB DRAM ]
  http://www.lsilogic.com/products/megaraid/scsi_320_2x.html  

LSI Logic MegaRAID SCSI 320-2E 2-channel U320 SCSI (PCIe)
[ 1/8-bit at 2.5GHz (0.25/2.0GBps), XScale IOP332, 128+MB DRAM ]
  http://www.lsilogic.com/products/megaraid/megaraid_320_2e.html  

LSI Logic MegaRAID SCSI 320-4X 4-channel** U320 SCSI (PCI-X)
[ 64-bit at 66-133MHz (0.5-1.0GBps), XScale IOP321, 128+MB DRAM ]
  http://www.lsilogic.com/products/megaraid/scsi_320_4x.html  

**NOTE:  If you're thinking about 12 drives.  Avoid putting more than
3-4 drives on a single SCSI channel.

- Drives

Going with "commodity" disks isn't always the most recommended.
"Commodity" disk capacities are typically the 40, 60, 80, 120, 160, 200,
250, 300, 320 and 400GB capacities.

The more "enterprise" disks are capacities of 36, 73, 146GB.  They are
designed for 24x7 environments, with greatly reduced vibration and other
superior quality.

NOTE:  You _can_ get "enterprise" disks in SATA interfaces.  E.g., the
Hitachi 10000rpm 36GB and 73GB U320 SCSI products are sold by Western
Digital as its "Raptor" SATA products.  The price difference is ~$350
(U320 SCSI) to ~$200 (SATA) for the 73GB capacity.

- Enclosures

If you have 3-6U of internal space, you can fit 5-10 1" drives (5 in
each 3U).  I like the Enlight EN-8721 which comes in both U320 SCSI SCA
and SATA (which is SCA-like hot-plug) flavors:  
  http://twe.enlightcorp.com/products/server/detel.php?serial=42

The SATA version runs about $150, the U320 runs just over $200.

For external enclosures, SATA is just finally getting some.  The 1m
limitation to SATA is a major factor (something that will be solved by
Serial Attached SCSI, SAS, which uses the same physical interface as
SATA for maximum compatibility).

If you're thinking more like 12 SCSI drives (with the 320-4X), the
Enlight SE-301 is Intel SSI certified:  
  http://twe.enlightcorp.com/products/server/detel.php?serial=41  
  
On Mon, 2005-07-25 at 06:49 -0500, Bryan J. Smith wrote:
> And even when building a web server, I still recommend the "system"
> drive be RAID-10.  E.g., with an 8-channel controller, consider:  
> - 4-disc RAID-10 System
> - 3-disc RAID-5 Data
> - 1-disc Hot Spare (which can be used for _either_ ;-)
> With a 12-channel controller, make the RAID-5 data volume 7-discs.

Many times I'll actually just use RAID-1 for the system on an 8-channel
card.  E.g.,

 8-channel:  2-system (RAID-1), 5-data (RAID-5), 1-spare (either)
12-channel:  4-system (RAID-10), 7-data (RAID-5), 1-spare (either)

Otherwise, if the hardware is local to you, with a 3Ware Escalade card,
it can page you on a failure.  So if cost is an issue, get a 3Ware
Escalade 8506-4LP (sub-$300), one EN-8721 enclosure ($150), and put in 5
drives, knowing that one drive is not connected (but is "ready to plug"
in its can).


-- 
Bryan J. Smith                                     b.j.smith at ieee.org 
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