Error Enabling Tler
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Grinch Moderator Joined: May 29, 2011 Messages: 10,361 Thanks Received: 1,831 Trophy Points: 161 Location: WHO(1)ville, Unixland One of the problems with consumer-grade hard drives is that most tler zfs of them will hang in the event that they run into an error, and will
Wd Red Tler
internally retry the operation, possibly for a minute or more. For a desktop PC, where redundancy does not exist, this is the correct seagate tler course of action, because failure of a sector means loss of the data. Enterprise class drives typically support the ability to limit the amount of time a drive wastes trying to recover data. Most of these drives are used tler wd green in RAID arrays, and so in the event of a failure, the data can be recovered from parity. A drive encountering read errors cannot be allowed to hang for large amounts of time, because this stalls whatever the server is trying to do. So manufacturers include features to control the retries of failures. For Western Digital, this is called TLER - Time-Limited Error Recovery. Great PDF. For Seagate, it is called ERC - Error Recovery Control. Samsung and
Tler Software Raid
Hitachi call it CCTL. Some people are confused and think that these features are only necessary for hardware RAID, or aren't useful for software RAID. It is absolutely true that this is a very important feature for hardware RAID, because a hardware RAID controller is probably configured to deem a "hung" hard drive as failed and to place it in an offline or recovery status, which has many negatives associated with it. So you absolutely do want TLER/ERC/etc for a hardware RAID setup. But what about ZFS? If you've got a ZFS pool, and your underlying disk device appears to hang for a minute, you probably stop serving up data. This is likely to be bad behaviour for a filer. Unlike a hardware RAID controller, ZFS will typically wait for the command to complete, and if it is trying to read many sectors, this could take a very long time. So TLER/ERC/etc are also desirable properties for a ZFS system. We've been thrilled in recent years to see the addition of "NAS" class hard drives, which are essentially conventional consumer-grade hard drives that have firmware that defaults to supporting TLER/ERC. You can verify that a drive has TLER/ERC turned on by probing it with smartctl. Code:# smartctl -l scterc /dev/ada0 smartctl 6.3 2014-07-26 r3976 [FreeBSD 9.3-RELEASE-p8 amd64] (local build) Copyright (C) 2002-14, Bruce Allen, Christian Franke, www.smartmontools.org SCT Error Recovery Control:
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Disable Tler
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Technology - unRAID Server Community » Legacy Support (unRAID 5 and Older) » General Support (V5 and Older) » TLER (Time https://lime-technology.com/forum/index.php?topic=1281.0 Limited Error Recovery) « previous next » Send this topic Print Pages: [1] Go Down Author Topic: TLER (Time Limited Error Recovery) (Read 4594 times) bubbaQ Global Moderator Hero Member Posts: http://www.24hourdata.com/blog/how-does-your-raid-array-handle-error-recovery-prevent-data-loss 3428 TLER (Time Limited Error Recovery) « on: December 30, 2007, 11:12:02 AM » I have seen some problems discussed elsewhere concerning RAID issues using desktop drives rather than raid-specific error enabling drives. The problem is with error recovery typically done by desktop drives when they hit a bad spot, that causes them to timeout and be dropped from the array as failed. (Anyone who experienced a failing desktop drives knows that your apps can hang for 15-20 seconds while the disk retries a bad spot.)Raid-specific drives have features to limit the error enabling tler retries so the drive will give up more quickly on a bad spot (such as Error Recovery Control (ERC) on Seagate drives , Time-Limited Error Recovery (TLER) on WD drives, and Command Completion Time Limit (CCTL), used by Samsung and Hitachi).Does unRAID's customizations to the MD driver account for this? If not, should it? Logged limetech Administrator Hero Member Posts: 5669 Re: TLER (Time Limited Error Recovery) « Reply #1 on: December 30, 2007, 02:02:04 PM » Account for it in what manner? Logged bubbaQ Global Moderator Hero Member Posts: 3428 Re: TLER (Time Limited Error Recovery) « Reply #2 on: December 30, 2007, 05:42:18 PM » What timeout does unRAID/MD use to flag a disk as failed? A shorter timeout typical of RAID arrays is 8 seconds, while a typical desktop system would be 15 seconds or more. If a typical RAID system timeout of 8 seconds is employed, and there are desktop disks in the array with extended error correction found in typical desktop drives, the drive could be doing error recovery for longer than the 8 s
help reduce the likelihood of a failed hard drive, data loss, and a data recovery emergency. The hard drives from popular manufacturers, including Western Digital and Samsung/Hitachi, all have different features that permit the system administrator, or whoever has configured the RAID array to configure how long a drive's firmware can spend recovering from a read or write error. Western Digital calls this Error Recovery Control (ERC), while Samsung/Hitachi calls it Time-Limited Error Recovery (TLER). The generic name for this feature in other hard drives is Command Completion Time Limit (CCTL). The idea is to limit the on-drive recovery time, leaving recovery to the RAID controller to prevent the possibility of performance degradation, which can lead to hard drive failure and, ultimately, RAID failure and the loss of mission critical data. What Are the Best TLER or CCTL Settings? Western Digital drives ship with TLER enabled at zero seconds, which means the hard drive itself will perform error recovery only in microseconds, well before the RAID controller's time out threshold. If TLER is not enabled and the drive times out, the RAID array will have to be re-built and re-synchronized. Enabling TLER, or, in other cases, CCTL or ERC, creates a more stable RAID array. TLER and CCTL in Stand-Alone Hard Disk Drives If you are operating a hard disk drive independent of a RAID array, you'll want to disable TLER for greater reliability, permitting the hard disk's firmware to repair any errors as it is able. Hard disks are designed to correct for small read/write errors that may occur. If read/write errors occur consistently and cannot be fixed by the drive's firmware, you could be facing a data recovery emergency. While you can still read files from the disk, create a back-up, and then change out your hard drive before it fails completely. Missed Your Chance to Create a Back-up? Often, we don't realize we are facing a potential hard disk failure until it is too late and our hard drive fails to boot. If this happens, don't worry. Pow