Disk usage policies on the ACCRE cluster establish individual account limits on both the amount of disk space used and the number of files stored on disk. Excessive numbers of files per unit of disk space have a negative impact on disk input/output procedures and significantly increase the tape backup load of files on home directories. For these reasons, users that need additional file quotas (without additional disk usage needs) must make special arrangements with ACCRE.
Automated enforcement of soft and hard limits have been established for both elements of disk usage. The following general definitions apply:
Soft quota: Baseline value for general usage limits. Soft quotas may be exceeded for brief periods of time, after which write permissions are automatically suspended until the user deletes enough to bring the account back under quota. Further details below.
Hard quota: Absolute maximum value. The system does not allow you to exceed this, i. e., you will receive errors if you attempt further writes to disk.
To help keep the system running smoothly, you should be in the habit of checking your usage level. Our FAQ explains how a user may check current disk space usage and quotas.
A summary of the soft and hard limits on disk space and files are outlined below, followed by a more detailed presentation of those policies. Subsequently, options for purchasing additional disk space and file limits are presented. Disk space will be allocated for the home directories with the assumption that all of the space could theoretically be in use (i.e., home disk space will not be oversold). However, because scratch space use is (by definition) assumed to be sporadic and temporary in nature, we may allocate more hard quota scratch disk space than is actually available on the system (i.e., oversell hard quota scratch disk space). We will not oversell the soft quota allocations of scratch disk space. Because of the special nature of the scratch environment, we devote a specific section to detailing the management policies for that space.
The True incremental Backup System (TiBS) is used to backup the ACCRE cluster home directories nightly. Currently the Quantum ATL P7000 Tape Library is used for the cluster disk backup. A big advantage of TiBS is that it minimizes the time (and network resources) required for backups, even full backups. After the initial full backup, TiBS only takes incremental backups from the client. To create full backups, an incremental backup is taken from the client. Then, on the server side, all incrementals since the last full backup are merged into the previous full backup to create a new full backup. This takes the load off the client machine and network. The integrity of the previous full backup is also verified. (TiBS is available for all current operating systems and apart from the cluster, ACCRE also offers backup services for data located remotely. This service is through special arrangement. If you are interested, please see our Tape Backup Services and contact ACCRE Administration for more details.)
Data Recovery from Backup
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ACCRE provides tape backup services for data stored on home. Data stored on scratch is not backed up. Backups are normally completed daily and restores are done upon request via Request Tracker. ACCRE does not guarantee that backups will occur daily and is not responsible for damaged tapes.
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If demand is unusually high on a given day (resulting in the inability to complete the daily backup within 24 hours), the next day's backup may not occur. However, prior incremental backups will continue to be available for restoration requests. This backup service is not designed for archival storage; rather, this service is for the recovery of user files lost due to corruption and/or accidental deletions.
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ACCRE offers restores for cluster users of files on home Monday through Friday, excluding Vanderbilt holidays, from 8:00 a.m. until 4:30 p.m. File restore requests are processed during these same hours by submitting a request via our support pages. Unless notified otherwise, restores will occur by the end of the next business day. In some cases, a restore may be completed on the same business day.
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Users may receive up to two free one-hour restores in any given fiscal year. Additional restores in any given fiscal year cost $100 per one-hour restore.
| Default Quotas per Individual | ||||
| Quota Type | Soft | Grace Period | Hard | Backup |
| Disk Quotas on /home | ||||
| Disk storage space | 10GB | 7 days | 20GB | nightly beginning at 11PM |
| Number of files | 100,000 | 14 days | 200,000 | |
| Disk Quotas on /scratch | ||||
| Disk storage space | 10GB | 14 days | 100GB | not backed up |
| Number of files | 100,000 | 14 days | 1,000,000 | |
Files on home directories are backed up nightly (beginning at 11pm). Full backups are kept for three months. Therefore, restorations of files are available for three months prior to the current date only.
The following disk space usage limits are implemented by default:
- Soft quota per individual account: 10 GB
- Hard quota per individual account: 20 GB
The soft quota may be exceeded for up to 7 days. After 7 days, the current disk space used becomes the hard limit. That is, you will only be able to read and delete files on your account until the total amount of disk used falls below the soft quota for the account.
Please be aware that excessive numbers of files per unit of disk space have a negative impact on disk read/write procedures and significantly increase the tape backup load of files on home directories. The following limits on the maximum number of files in home directories are implemented by default:
- Soft quota per individual account: 100,000 files
- Hard quota per individual account: 200,000 files
The soft quota may be exceeded for up to 14 days. After 14 days, the current number of files becomes the hard limit. That is, you will only be able to read and delete files on your account until the total amount of files in your home directories falls below the soft quota for the account.
Files on ACCRE scratch disk space are NOT backed up.
The following scratch disk space usage limits are implemented by default:
- Soft quota across all scratch directories owned by your account: 10 GB
- Hard quota across all scratch directories owned by your account: 100 GB
The soft quota may be exceeded for up to 14 days. After 14 days, the currently used scratch disk space becomes the hard limit. That is, you will only be able to read and delete files on your scratch disk space until the total amount you are using falls below the soft quota limit for that space.
As noted above, excessive numbers of files per unit of disk space have a negative impact on disk read/write procedures and significantly increase the tape backup load of files on home directories. The following limits on the maximum number of files in scratch directories are implemented by default:
- Soft quota across all scratch directories owned by your account: 100,000 files
- Hard quota across all scratch directories owned by your account: 1,000,000 files
The soft quota may be exceeded for up to 14 days. After 14 days, the total number of files currently in your scratch space becomes the hard limit. That is, you will only be able to read and delete files from that space until the total number of files falls below the soft quota limit for that space.
Options for increasing disk quotas and file limits, as well as their associated costs, are described below. Requests for increases in disk space and/or file limits are evaluated by ACCRE personnel on a case-by-case basis. Resources must be available for a given request and need must be demonstrated. Upon approval and receipt of funds, increases will be in effect for up to one year. Please initiate your request via Request Tracker.
There is a $25.00 processing fee for each increase request.
Soft and hard quotas:
- There is a default buffer of 10 GB between the soft quota and the hard quota. When you pay to increase your soft quota, your hard quota is 10 GB higher than your soft quota automatically.
- Because of the standard buffer (10 GB) between the soft and hard quotas, as well as the fact that neither soft nor hard quotas are being oversold on the home directories and that backup costs are standard for all home disk usage, all purchases of additional home disk space are for increases in soft quotas. The minimum cost is $4.56 per additional GB per year ($3.00 for disk space plus a minimum of $1.56 for backup). Depending on the typical backup compression ratio for your files, your backup costs per GB may be substantially higher than the minimum.
Number of files:
Increases in the number of files allowed are proportional to increases in disk space. That is, an increase of 100,000 files is allowed per GB increase in space. For example, an increase in 10 GB soft quota will result in an 100,000 soft quota file increase. The buffer between the soft and hard quota limit will remain the same (100,000 files), because the disk space buffer remains the same (10 GB).
There is a $25.00 processing fee for each increase request.
Soft quota:
- With a demonstrated need, your scratch soft quota limit may be increased to 25 GB at no cost and the processing fee will be waived. Subsequent increases in soft quota limits cost $3.00 per additional GB per year.
- There is a default buffer of 90 GB between the soft quota and the hard cost. When you pay to increase your soft quota, your hard quota is 90 GB higher than your soft quota automatically.
Hard quota:
- Increases in scratch hard quota limits are available at a rate of $1.08 per additional GB per year.
- The cost per GB for the hard quota is less than the cost per GB for soft quota because the total amount of all space allocated for soft quota disk space is never greater than total allotted disk space. The amount of all space allocated for hard disk quota space if every user was simultaneously using their total allotment can be greater than available disk space.
Number of files:
Increases in the number of files allowed are proportional to increases in disk quotas. Thus, assuming that 10 GB in additional soft quota scratch disk space is required and purchased, the maximum soft quota file limit will increase by 100,000 files; the addition of 10 GB in hard quota scratch disk space will result in an increase of 1,000,000 files on the hard quota limit.
