SATA Experiences HEPiX Spring 2005 Fermilab Ray Pasetes, Lisa Giacchetti

Type Of Storage  Enterprise Typically SCSI or Fibre Channel Typically SCSI or Fibre Channel Very expensive, high performance Very expensive, high performance  Mid-Tier Enterpise SATA, FATA Enterpise SATA, FATA Higher MTBF than commodity Higher MTBF than commodity 90-95% streaming performance of Enterprise drives 90-95% streaming performance of Enterprise drives  Commodity SATA, ATA, IDE SATA, ATA, IDE 90-95% streaming performance of Enterprise drives 90-95% streaming performance of Enterprise drives

Types of SATA storage  FC Controllers, SATA storage Sierra Logics ATA-FC bridges Sierra Logics ATA-FC bridges Custom ASICs Custom ASICs  PCI/PCI-X controllers Most RAID Most RAID Some JBOD Some JBOD

You Get What You Pay For  Firmware Fixed 512B blocks Fixed 512B blocks No checksum per driveNo checksum per drive Bad block allocation timeouts Bad block allocation timeouts Some ATA/IDE/SATA fw allows for 2 minutesSome ATA/IDE/SATA fw allows for 2 minutes Head misalignments Head misalignments Common for disks with high idle times while poweredCommon for disks with high idle times while powered Single processor for head movement and data movement Single processor for head movement and data movement Higher activity in one causes the other to degradeHigher activity in one causes the other to degrade Hot Spots Hot Spots Data corruption Data corruption Data checksummed and verified accurate at time t1, read back corrupt at time t2.Data checksummed and verified accurate at time t1, read back corrupt at time t2.

You Get What You Pay For (2)  Dual Controller – just two words May not mean controllers failover (at all ) May not mean controllers failover (at all ) Each controller only handles ½ of RAID.Each controller only handles ½ of RAID. May not mean controllers failover automatically May not mean controllers failover automatically System needs to be reset to have surviving controller take over.System needs to be reset to have surviving controller take over. May not be available May not be available Option does not exist.Option does not exist.

You Get What You Pay For (3)  Stability of Unit May find self as un-willing beta tester May find self as un-willing beta tester FW updates introduce more problems than fixesFW updates introduce more problems than fixes FW updates fix problem, breaks other features that were workingFW updates fix problem, breaks other features that were working Often find bugs already known but not disclosed Often find bugs already known but not disclosed Loss of data not as rare as one would expect Loss of data not as rare as one would expect  Upgrades are disruptive

Under Investigation  Enterprise class “S/ATA” solutions EMC EMC Still uses 250GB, 5400RPM PATA drivesStill uses 250GB, 5400RPM PATA drives LSI LSI 250GB, 7200RPM SATA250GB, 7200RPM SATA 1.25TB, 5400RPM SATA blades1.25TB, 5400RPM SATA blades HDS HDS 250GB, 7200RPM SATA250GB, 7200RPM SATA  Vendors slow to adapt to new technology None offer 400GB drives. None offer 400GB drives. Some claim 400GB drives show 1/8 reliability in internal testing. May never adopt this drive. Some claim 400GB drives show 1/8 reliability in internal testing. May never adopt this drive.

Under Investigation (2)  Tweaked SATA storage FW changes FW changes Allows for 520B blocks – can checksum per driveAllows for 520B blocks – can checksum per drive Periodic head sweeps – prevents hot spots, misalignmentsPeriodic head sweeps – prevents hot spots, misalignments Perceived “better” testing of sw, hw, fw.Perceived “better” testing of sw, hw, fw. Some claim drives not available in open market Some claim drives not available in open market  Upgrades are non-disruptive (dual-attach)  More expensive…but not too outrageous

Understand Your Needs  Caching storage Massive storage Massive storage Loss of disk access and data tolerable Loss of disk access and data tolerable Data also on tape or other storage mediumData also on tape or other storage medium Low I/O. Low I/O.  Secondary storage Loss of disk access somewhat tolerable Loss of disk access somewhat tolerable Downtimes allowable, usually off hours.Downtimes allowable, usually off hours. Loss of data NOT tolerable Loss of data NOT tolerable Low I/O Low I/O