Sata on Evan Hoffman

Rescan SATA bus (aka hot-adding a SATA disk on a Linux guest in VMware without rebooting)

Mon, 24 Oct 2011 15:20:51 +0000

Linux supports hot-adding disks but whenever I add a new vdisk in VMware the new disk doesn’t show up unless I reboot, which defeats the purpose of hot-add. This command forces a rescan of the bus:

echo "- - -" > /sys/class/scsi_host/host0/scan

dmesg shows the new disk has been found:

Vendor: VMware Model: Virtual disk Rev: 1.0 
 Type: Direct-Access ANSI SCSI revision: 02
 target0:0:2: Beginning Domain Validation
 target0:0:2: Domain Validation skipping write tests
 target0:0:2: Ending Domain Validation
 target0:0:2: FAST-40 WIDE SCSI 80.0 MB/s ST (25 ns, offset 127)
SCSI device sdd: 1048576000 512-byte hdwr sectors (536871 MB)
sdd: Write Protect is off
sdd: Mode Sense: 03 00 00 00
sdd: cache data unavailable
sdd: assuming drive cache: write through
SCSI device sdd: 1048576000 512-byte hdwr sectors (536871 MB)
sdd: Write Protect is off
sdd: Mode Sense: 03 00 00 00
sdd: cache data unavailable
sdd: assuming drive cache: write through
 sdd: unknown partition table
sd 0:0:2:0: Attached scsi disk sdd
sd 0:0:2:0: Attached scsi generic sg3 type 0

Now, why there’s no “rescan_sata” command is something I can’t fathom, but that’s Linux for you.

The bright side of Compellent

Wed, 22 Sep 2010 16:07:46 +0000

Since I was bemoaning Compellent’s pricing recently I figured it would be unfair of me not to highlight the upside. Their tagline is (or was when we purchased it) “The only SAN so sophisticated it’s simple.” While I can’t say whether they’re the ONLY one, the idea is definitely true. This is the first SAN I’ve ever used, and aside from the learning curve for iSCSI itself (targets, spinup delay, etc.) it’s totally simple and intuitive. Create LUNs, map them to servers. Don’t worry about things like RAID levels or hot disks. We’re into our second year with Compellent and it’s definitely lived up to its promise of simplicity.

Oh, Compellent... again with the disk prices.

Wed, 25 Aug 2010 00:57:04 +0000

Time to expand the SAN again.

I planned and budgeted for this this year but it still pisses me off. Look, I realize these guys have to make money, but the bottom line is they’re charging over $1.40/GB for SATA storage. There are 7200 RPM 2TB SATA drives on Amazon and Newegg ranging in price from $130 to $220. That’s as low as $0.065/GB. There was even a 2TB WD “Green” drive (sub-7200 RPM, I think 5900 RPM) on Slickdeals today for $99. That’s 5 cents per gig.