SAS all the way. Think of it as fibre channel, that you can afford.
You can also mix SATA and SAS disks so really the biggest difference
between SATA II and a SAS is the cost of the host bus adapter (HBA).
I don't have personal experience with external storage for SAS
(expanders) though I haven't heard anything negative about them. You
can support 100's of disks in SAS via expanders. Regarding
credentials, I work on the adp94xx driver for Stratus Technologies.
Though don't take my word as gospel, prove it to yourself that the
extra money for the SAS HBA is worth $1000. To give you an idea on
performance.
[rhod<05:37:38>]# lspci | grep Adaptec
07:00.0 Serial Attached SCSI controller: Adaptec AIC-9410W SAS (Razor
ASIC non-RAID) (rev 09)
7a:00.0 Serial Attached SCSI controller: Adaptec AIC-9410W SAS (Razor
ASIC non-RAID) (rev 09)
[rhod<05:30:59>]# lsscsi
[12:0:128:0] disk SEAGATE ST373455SS 0002 /dev/sda
[12:1:128:0] disk ATA ST3250620NS 3.AE /dev/sdb
[12:2:128:0] disk ATA ST3500630NS 3.AE /dev/sdc
[13:0:128:0] disk SEAGATE ST373455SS 0002 /dev/sdd
[13:1:128:0] disk ATA ST3250620NS 3.AE /dev/sde
[13:2:128:0] disk ATA ST3500630NS 3.AE /dev/sdf
Keep in mind that the disk cache is set to write-through to avoid data
corruption if
the disk is pulled or the HBA disappears.
[rhod<05:31:05>]#
[rhod<05:31:05>]# hdparm -t -T /dev/sda
/dev/sda:
Timing cached reads: 9604 MB in 2.00 seconds = 4802.73 MB/sec
Timing buffered disk reads: 376 MB in 3.00 seconds = 125.23 MB/sec
[rhod<05:31:26>]#
[rhod<05:31:26>]# hdparm -t -T /dev/sdb
/dev/sdb:
Timing cached reads: 10576 MB in 2.00 seconds = 5288.80 MB/sec
Timing buffered disk reads: 230 MB in 3.01 seconds = 76.42 MB/sec
[rhod<05:31:45>]#
[rhod<05:31:45>]#
This version doesn't support NCQ so that's why sdb is such a dog. sda is also
a 15K disk where sdb is only 7200 RPM. I haven't tested the upstream
driver as to how well NCQ works, I'm still working on RHEL4.5.
When it comes to raid we use md (level 1) because of it's flexibility
so I couldn't attest to the hardware raid performance of the HBA.
If you're interested in the ability to hotplug your HBA, that feature will
be available shortly :-).
Peter
On 8/20/07, Scott Ehrlich <scott@xxxxxxx> wrote:
> I have a Dell PowerEdge 2950 and am looking to add more storage. I know a lot
> of factors can go into the type of answer given, but for present and future
> technology planning, should I look for a rack of SATA, SCSI, or fibre channel
> drives? Maybe I'm dating myself with fibre channel, and possibly SCSI?
>
> I may be looking to add a few TB now, and possibly more later.
>
> What are people using these days? What throughput and reliability are you
> seeing? What accounts for the cost differences?
>
> Thanks.
>
> Scott
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>
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